I use the recent Ganymede release of Eclipse, specifically the distro for Java EE and web developers. I have installed a few additional plugins (e.g. Subclipse, Spring, Find
Eclipse generally keeps a lot of meta-data in memory to allow for all kinds of IDE gymnastics.
I have found that the default configuration of Eclipse works well for most purposes and that includes a limit (either given explicitly or implictly by the JVM) to how much memory can be consumed, and Eclipse will stay within that.
Is there any particular reason you are concerned about memory usage?