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
Well, you don't specify on which platform this occurs. The memory management may vary if you're using Windows XP, Vista, Linux, OS X, ...
Usually, on my computer (WinXP with 1Gb of Ram), Eclipse take rarely more than 200Mb, depengin of the size of the opened projects, the loaded plugins and the ongoing action.