Just bought a 16GB Patriot LX Class 10 card. It won't write to it... formatted from the phone a couple times, no luck. Trying to format now in Windows.
My old 8GB no-name card worked perfect :/
And my fault, didn't read the reviews before buying. Luckily it was dirt cheap and i can still use it:
Amazon.ca: Customer Reviews: Patriot LX 32 GB Class 10 MicroSDHC Flash Memory Card PSF32GMCSDHC10