I've been using a cheap(well Staples was selling them for $10 at one time which was VERY good for b&m and it was convenient) PNY class 4 4GB uSD SDHC w/no problems, reboot etc.
I actually bought 5 of these when they had them for $10(now $15 last I checked, i.e. ripoff -- $10 was a little high but for convenience of b&m it was good) and have been using them in several devices: Viewsonic gTablet, Archos A43IT, Kobo WiFi reader(w/SD card adapter), and for about a week or so now in my Optimus V.
Might was to avoid class 2 unless they're super cheap, and just generally run far far far away from cards made in China as they are the poorest quality by far with Japan best followed by Taiwan. (If the uSD says Toshiba it was made in Japan as that's their only plant. Also ANY card that says made in Japan is made by Toshiba as not only is their only plant there, it's also the only one in Japan...)
Class X just means that the mfg is SUPPOSED to ensure that X MB/s WRITE speed is guaranteed under ALL conditions and that is it. i.e. there is no guarantee about read speeds, latency, etc.
This is about all I can say ATM as 16GB uSD are still somewhat high priced IMO, and I haven't see uSD prices budging in about a year now which is kind of odd... 16GB might be overkill unless you're rooting or running custom ROM and plan on doing apps2sd OR are going to load it up with LOTS of media files, i.e. music/video
Right now I'm debating buying a few 8GB class 6 uSDs from newegg but keep hoping that prices start dropping again...
[EDIT]
Oh yeah, those PNY cards that I got, Taiwan... they're OK but Japan/Toshiba are the best... and DO run away from China cards as they're generally garbage and do NOT buy uSDs from Chinese vendors as they sell TONS of faked cards, i.e. cards that've been re-programmed to claim that they're higher capacity/speed than they really are...
[/EDIT]
