The latest OS 2008 has no problems with ext3. I formatted a memory card with ext3 and was able to use it on the tablet without having to load any driver modules manually. Automatic mounting / unmounting went fine, too.
There's really no reason to use FAT32 on your memory cards, unless you want to be able to read the card on non-Linux systems.
Of all filesystems that are around today, FAT is definitely one of the worst and most unreliable.