I can agree with the ubuntu starting to have problems. They moved to unity with 11.04 and did not make the OS very impressive. I will be installing gnome3 if I can.

Mint 10 works good and so far, not had one problem--maybe I am just careful. If mint 10 works stick with it. I liked ubuntu 10.10 better than 11.04 anyway.

Arch is when it is time for a new challenge. If you up to it, see how well you do.
Try using wicd to setup wireless networking. If you can connect via wire, then you can install wicd online. Hope everything works out.

Any distro can be installed on a usb drive. Pick the one that you like most. don't think you can make a dualboot usb. You can install distros on a VM client like virtualbox to try out multiple distros.

Actually, I have heard of of folks dual and triple booting off of a usb. I was never really interested in the process, so I didn't keep links, but in theory, it is possible. Installing directly onto the usb and partitioning it before the installation with something like ext2, as long as you have enough room, and can make enough partitions large enough, I'd say it was possible. When I installed Sid onto a 4gb stick with persistence a few years back, I just had to make sure that I installed grub to the mbr of the stick. Once grub is written to the mbr, if you created extra partitions during the first install, you could add another distro. I really haven't done a live usb install for some time so I might be way off base, but, I have read of others doing it. Maybe Auntie Google can find those threads.