Finally a copy and paste application! Although it's in beta, Clippy is now available on Cydia. At the moment, it can only copy and paste text from text fields in Safari, but it has full support for Notes and Mail (maybe more). Hit 123 on the keyboard and Copy and Paste will come up. The only thing is, you use the text navigation thing (drag over text) to select, so you can't go to the middle of a word and backspace/add text anymore... I'm not sure if they'll change that.