I remember there being a debate up here when I first joined, about whether or not to allow Firefox Portable to support multiple users like the installed one does.
The argument for is pretty obvious. Separate logins for the same site was one. Gmail was a good example of this for me until I discovered the Gmail Manager extension; cookie swappers also exist but that's sloppy. Or multiple users. The argument against held that flash drives should be personal, one to a person, your friend can get his own and they're cheap enough.
It really isn't hard to hack if you want more than one profile. It doesn't take as much work as I do, I just do it rather cleanly. First, I renamed my Profile folder to profile_WORK. Then, I made a new profile called profile_NATHAN and then did it again for my wife. I opened up EditPad (my text editor at home) and made a blank file in each with the name, in case I got confused, e.g. __NATHANS_PROFILE, __WORK_PROFILE, etc. So now you go into one or the other and that top-listed file is the first thing you see. To change from one to the other, I simply apply the missing label to the Profile folder, and rename the one I want to start using to "profile".
Simple solution. My wife and I went to a Rock Band 2 tournament on Saturday (placed 3rd, yay) and we thought we might have time to stop in a computer lab, so we wanted our home profiles on the go. We didn't need them, but I needed my own home profile at work the other day, so it was good to have it.
Just thought I'd put that out there for anyone who still wants the multiple profiles.