Originally Posted by murg
I've been wondering this also...
But I just did some research and my conclusion is that it's not easy to buy fast microSD cards. They do advertise "class" - which is max sustained read/write speed - but in random access (which is what matters for non-camera usage) it's all over the place, which higher class often (but not always) worse.
If you look at random access 4 KB-block-sized writes, various cards can achieve anything from 2 MB/s (500 blocks written per second) to 0.006 MB/s (yes, 1.5 blocks written per second).
There exists at least one Sandisk 2 GB class 2 model which is incredibly fast, and if Kobo actually ships with that model, it's going to be hard to beat.