Update: Not a fan of Umbrello has a lot of features for UML but too many functionality gotcha's and bugs (from a user stand point I can't comment on it's UML implementation because I'm a newb on UML)

I ran into the can't a Anchor a Note to an Activity with error "Incorrect use of associations". I tried installing it under Debian 6.x but even with the downgrade of Fedora 17's version 2.8.4 to Debians version 2.4.5 of Umbrello it's still wouldn't do it while drawing an Activity Diagram (and this is despite the Umbrello Handbook showing a working example).

So I failed back to Dia which suprisingly had all the shapes and connectors required to do what I was trying for. The end result was pretty good.

http://www.umbrello.org/

I'm interested in doing flow charts (which UML calls Activity Diagrams) but ultimately modelling complex programming behaviours with an eye to coding more logically.

Just installed Umbrello and discovered I had no icons on my menu buttons

I don't know if this is the right thing to do to fix it but it worked for me:

yum install kdesdk

Icons are back.