I run Kubuntu Jaunty with KDE4 on my netbook. BasKet wasn't doing it for me so I tried to get Tomboy happening. Problem was, it would abort with a SIGSEGV and complain about errors in mono any time I tried to run it. I couldn't find anything out there that suggested a workaround, so I set about building a newer version than was in the repos from source. Couldn't get that happening, but in my travels I installed the package gnome-doc-utils and BAM, it worked.
So, if you're having issues with Tomboy refusing to start under KDE4, have a crack at:
sudo apt-get install gnome-doc-utils
Let me know in comments if it does the trick.