Hey
I have another suggestions:
1) On class diagram - it would be much easier if I could add a new operation/attribute while adding previous one by CTRL+ENTER on keyboard. Also by pressing INSERT on keyboard while operation/attribute is selected, then new op/att should be inserted below selected one.
2) On class diagram - if operation/attribute is selected, pressing DELETE on keyboard should delete this selected op/att, not whole class.
3) All diagrams - You really ought to implement "lock element", for instance look at Visual Paradigm. What they done there is quite good.
4) On Class Diagram - when I'm typing class name like that "<<struct>>Name" then "struct" should be moved to stereotypes automatically.
5) On sequence diagram - by default objects shouldn't be named (eg. "object1") (left black) In most cases on sequence diagrams instances names aren't important.
6) On sequence diagram - then there's "bar" on object's life line (control) and there's another invocation on this object, new "bar of control" should be moved on right, not lying on the old bar. (Sorry for my english ;)

Regards
Andrew