* use different modern file systems (ext3, NTFS, reiserfs, zfs, HFS+ etc) with their extra features (POSIX, permissions, compression, efficient storage for small files, encryption - important for a mobile device, versioning or backup etc) to store or sync files with their desktop
Please have a look at my loop-device solution in the brainstorm. It already works flawlessly on my N900 .... The images are sparse files, i.e only allocated sectors in the disk image are actually allocated on the ext3 fs and free space is not wasted.
Its much easier to resize an optional disk image than a crucial partition which holds most of your apps and your home.