I prefer to run 32 bit java on my desktop since I only have 2GB of RAM. 64bit buys me nothing, and it eats twice the RSS.
With Jaunty (and Gutsy before that) I'd followed derek's advice on building a 32bit .deb.
I ran a downloaded 32bit eclipse.
Karmic seems to have broken something (probably SWT) and 32bit eclipse with 32bit JDK isn't usable.
Posting this here so I can find Derek's article again and start with that to get 32bit eclipse and 32bit sun-jdk working together again.
[update] It looks like Miroslav Hruz has a solution to the 32bit SWT issue. I'll try that on the weekend (remotely).
[update] I got things working without really understanding (or logging) what I did. After a bunch of uninstall, reinstall, all without notes (and some of it was in synaptic, so not in .bash_history), 32-bit sun-jdk and 32-bit eclipse started working again without me needing to do anything as in the links above. I did export GDK_NATIVE_WINDOWS=1 though. Thus ends this unhelpful post :-).