I bought one of those Samson USB mics a while back, and while it's nice to just plug the thing into a computer and go, I'm not really that impressed with it. Particularly since - the last three times I've tried to use it - it's had an annoying static noise that I haven't been able to isolate.
Compound that with problems getting it working in the first place (on a Mac) and I can't really recommend it.
But if you are in the market for a USB microphone, then check out the April issue of Electronic Musician, which has an article comparing six different USB mics.
My own perspective: I have a Line 6 Toneport USB box which I use with 'real' microphones, and while it's a little more baggage to work with, the results are much more consistent and satisfactory.