The 500GB SATA drive in an external enclosure that I use for backups (eSATA/USB 2.0 connectivity) is currently NTFS-formatted for compatibility reasons. I would much prefer to use ext3 or HFS+, but it's pretty hard to get those two working correctly on all operating systems. Thanks to NTFS-3G and (Mac)Fuse, I can reliably access NTFS partitions on Linux, OS X and Windows (of course) so it's become my FS of choice when it comes to compatibility.

Unfortunately, that means that the drive becomes horribly fragmented (and pretty quickly, too). I decided to do a defrag today and found that the NTFS partition was 38% fragmented with 78% file fragmentation... Yuck. I'm going to be really happy when there's a filesystem that I can use on all operating systems that doesn't fragment or choke all the time. Ext2/3 was looking like a pretty good for the "doesn't fragment" part, but the ext2fsx project for OS X seems to have died out and ext2fsd, the only driver I've found for Windows that supports ext3 filesystems with inode sizes > 128, tends to bluescreen a lot. Back to waiting, I guess...