you will see the end of this page
https://bugs.eclipse.org/bugs/show_bug.cgi?id=385272
1) Help>Install New Software
2) use the site: http://download.eclipse.org/eclipse/updates/junoSR1Patch-tmp
3) select Eclipse UI Juno SR1 Optimizations, install, and restart
this will make eclipse 4.2 work faster when you change tabs in xml files. that was bugging me for a long time.
cheers 🙂