[ale]

I've always remapped ctrl+r to U as u (undo) and U (redo) feel more consistent with other shortcuts. I suspect this already is very common.

[ryanmcbride]

I do the same, the ctrl+r always seemed strange to me for this

[stvltvs]

Because U was already used in vi, although that form of undo isn't super helpful IMHO. Both R and r are also already used, so Ctrl-r for redo it is.