Eric S. suggests in http://www.schabell.org/2010/02/jboss-developer-studio-performance.html and http://www.schabell.org/2010/02/jboss-developer-studio-300rc1.html that adding the following to eclipse.ini
-XX:-UseParallelGC
-XX:+AggressiveOpts
-XX:-UseConcMarkSweepGC
Makes the startup significantly faster.
I could not reproduce the results on Java6/Windows 7 combo but it would be interesting to see if it does make a differences on other machines since my machine is broken in other ways.