@jacktanner,

The class number is not really a standardized, formalized, classification. Meaning anyone can almost give whatever class they want to their cards.

Class 10 means the card can be written to *sequentially* at 10Mb/s or more. This is useful if you record HD videos on the card (i.e. for a digital video camera).

Some (most?) class 10 cards manage that, at the expense of a usually lower performance under random writes when compared to "lower" cards, such as class 2 or 4.

I have a Sandisk class 2 (or 4?, not sure now) card and it can do 10Mb/s when writing, perhaps not consistently, but I don't care. Performance for swap, as well as for a debian squeeze chroot I installed on an ext3 partition, is perfectly adequate.