Chances are, whatever grain you're using, QBrew has a listing for it in its database. This means that if you want to use 9 pounds of American two-row pale malt, QBrew already knows what that is, and has a number associated with it representing the average extraction rate and color for that kind of grain. Same goes for average alpha acid levels and alpha utilization rates based on time in the boil for different styles of hops. Most of your setup, then, would be limited to either adding grains or hops that don't exist in the database yet, or customizing extraction or utilization numbers in pre-existing database entries. QBrew provides a brain-dead simple interface for doing this, should you find it necessary.
In addition to these changes, you can also open the application's Preferences and change global options such as the color and bitterness scales used, as well as your brewing system's efficiency. The efficiency number is crucial, and can have a dramatic effect on how close you come to hitting the target gravity levels QBrew gives you in response to your ingredient list.
The opening screen in QBrew is geared toward immediate productivity. There are no wizards to get in the way of your goal of getting a useful recipe out of the tool. The main screen contains a top and bottom section. The bottom section is tabbed, and allows you to quickly and easily add different grains and hops. It also makes it easy to specify the extraction method used to get the sugars from the grain (including mashed, steeped, and others), as well as the alpha level and form of hops you're using.
One thing I really like about the interface for adding ingredients is that it allows you to override any of the numbers associated with a given ingredient on-the-fly. This is useful to home brewers, because there are many variables to account for in the brewing process that may cause you to want to alter these numbers on occasion. Sometimes we're forced to go to a different grain supplier, or use Fuggles hops that are 10.0% alpha instead of 8.6% alpha, or account for a particular inefficiency in our brewing systems. No matter what number you want to change, there's a text box for you displaying what the database says, which is editable for one-off adjustments.
The adjustments you make will not change the default values in the database. Though there's an interface for doing this, I find it more useful to keep that functionality out of the way. The value I find has to change most frequently is the alpha values for the hops. If I get hops that are normally 8% alpha but today my supplier has a batch that are listed as being 9.5%, I want to account for that in my recipe, but leave the default value alone, so that next time I get this hop at its normal level, I don't have to change it back.
In addition to hops and grain, there are also tabs in the input pane that allow you to specify the type of yeast used, any additives you might use (whether it's Irish moss or raspberry extract), and any notes you care to make. The Notes tab is usually where I put my mash schedule, yeast pitching notes, and boil additive schedule (if any).
While you're adding grains and hops to your recipe in the tabbed bottom pane, the top pane acts as a constant summary area which automatically updates itself every time you add an ingredient or change how it is used. For example, if you change the amount of time a hop is boiled, QBrew will adjust for the fact that the alpha utilization will also change. If you change the amount of base malt, it will change the specific gravity accordingly, and if you change a specialty malt, it will change the color. The summary area also keeps track of expected alcohol by volume and weight, estimated final gravity, and other numbers that are vital to developing the foundation of your recipe.
The summary pane also lists the maximum and minimum gravity, bitterness, and color levels according to standardized style definitions published by the Beer Judge Certification Program. This is useful if you're brewing for a competition, or you're trying to target a particular style of beer.
Once you've completed the tweaking of your recipe in QBrew, you can print out a copy that is nicely organized and neatly formatted, so if you can't have your laptop handy on brew day, you can at least have a printout of your plan. There's also plenty of room left on the paper to make notes about adjustments you make to the recipe during your session.
Though I use QBrew to help develop recipes, it's still not at the point of being a homebrewer's end-to-end tool. There are a lot of calculations involved in home brewing that QBrew hasn't accounted for. For example, I am not aware of a method to get QBrew to scale a recipe for me. If I develop a recipe for a five-gallon batch of beer, and it turns out wonderfully, I cannot go into QBrew and say "scale this recipe up to 10 gallons." It also will not calculate strike, step mash, and sparge water infusion volumes and temperatures, which are incredibly useful for homebrewers. I think most brewers, myself included, would consider these features basic, and would expect to find them in any brewer's tool.
Average yeast attenuation, flocculation, and temperature tolerance values are also not taken into account in the recipe development process. These calculations, along with an expected boil-off calculation, would also be useful, though they are perhaps less urgently needed than the aforementioned features.
Other brewing software tools even go beyond these basics to list minutiae like the mineral makeup of popular beer regions, which can help you figure out how to adjust your own water. Some of the great beer regions of the world brewed beers in accordance with what tasted best with their local water. The nearly mineral-free water of Plzen was wonderful for creating Pilseners, for instance, while the unique mineral-rich profile of London was perfect for brewing ales and porters.
Just brew it!
In the end, in spite of missing features, QBrew is still a useful tool for creating a "quick and dirty" recipe, and putting together a basic shopping list for your upcoming brew session. The one thing QBrew has over all other brewing tools I've seen is its ability to run on just about any platform you can name, which is a testament to the benefits of the open source development model, and a feature that no other tool can claim. While it's true that other tools can run on platforms other than Windows, the two most popular ones cannot do it without some intermediate software such as Wine or VirtualPC. I'd personally rather run native software for the important stuff, and find online tools to fill in the pieces that are missing in QBrew.