Sequence Diagrams

[mick]

It would be extremely useful to be able to select multiple messages on a sequence diagram, and then be able to either copy and paste them to another diagram, or move them within a diagram

[gpc]

Yep, it would be handy.
I usually copy the diagram and then remove the unwanted messages, which is easier than recreating from scratch.
(beware about things like notes though - they look like copies, but they're not! it's the same note, i.e. edit one and the other is changed automagically).