Can I use ext4 on my SD card in a non-rooted phone? I know that on a rooted phone, it's reasonably normal to create a small ext4 partition for App2SD to use, but I'm not asking about that case:  I have a non-rooted HTC Desire running Froyo, and I'd like to format the whole of my SD card as ext4 instead of FAT.  I'm aware that this will mean that Windows PCs won't be able to use the card, but all my PCs run Linux so they should be fine.  Will the phone be able to access and use the card in this case?
ext4 should be supported if you have an upgrade to 2.3 or 3.0 Android (I see that your post is from just before the 2.3 &amp; 3.0 releases...).

...and when btrFS is added to Android, it has a nice mount-option ",ssd" with wear-levelling etc that ext4 doesn't have... and more speed than ext4 now, esp if you use ",compress=lzo" OR ",space_cache" in fstab (but don't use compression WITH the space_cache option, only use 1 or the other or else it slows to a crawl in some benchmarks) -- and that speed comes despite btrFS checksumming of all data (not only of the journals, as ext4 does). :-)