I had a Pi running happish on a class 4, if I recall correctly... I just mounted the root file system read only and created a small ramdisk to /tmp. Whenever I needed to change something I would remount it rw, change, reboot. Before that the card would be killed every other week, every time the Pi suffered a power failure. Probably a slow card cannot flush the cache fast enough.

But I don't own it anymore, I sold it to a friend and now I am a proud owner of a cubietruck.