I tested the card's performance and saw 20 MB/s read and 12 MB/s write; not far off what Samsung are advertising. This is roughly the same as I get from the full-size 2 GB SanDisk Extreme III (also class 6) SD card I am using in my digital camera. I expect I will need that performance when recording 1080p video with my Galaxy S2.
For comparison, the same test with an 8 GB SanDisk (class 2) micro SD card yielded just 7 MB/s write performance, although the reads were the same (may be a limitation of the card reader in my PC).
The card also comes with a micro SD to full-size SD card adaptor, which I wasn't expecting. Not at all bad value for money. Highly recommended.