I have been using DeltaCopy (a rync GUI wrapper) for quite a while now. It works well.
But rsync and DeltaCopy aren't user-friendly. That, I feel is their biggest undoing.
For example, the retry count in DeltaCopy for a failed backup attempt is 5. That should be 1 (Edit->Modify Retry Configuration menu-item). If it fails once, then it would fail again and again.
Also, they would be better off making -i (itemize changes) and --modify-window=1 (don't write back a file if modify time is < 1 second). The latter option is particularly insidious. Until, I read the rsync FAQ, I didn't know what was the reason that the backup wasn't looking like an incremental one (quick and easy).
Oh, DeltaCopy automatically adds -rlt options to rsync command line which some tips pages refer as well.
I think, DeltaCopy owners lost the enthusiasm in perfecting the product - it works but it could have rocked.