In your workspace folder there is a file named .metadata/.log . It may give an indication as to what is wrong.
However, form what you describe this sound like the famous eclipse PermGen space problem (Eclipse is running out of class loader memory). It is fairly easy to fix. Edit the eclipse.ini file to add smt like:
I dont know if it is also happening to other people but I downloaded the last version of Lomboz (mainly in order to use the Liferay integration) but I have to say that it keeps crashing, and this on different occasions: opening a Java file, trying to use the auto completion, trying to edit a JSP... as I say, not always but I keep restarting it every 5 or 10 minutes.
Java: JDK 1.6
OS: Windows Vista Ultimate 64bits
RAM: 4 Gb
Somebody knows something about that?