Here is the memory usage of Eclipse when it is minimized BEFORE installing the plugin. Notice that even though I have 1GB in my machine and the VM size is over 100MB, the physical mem usage is only 4MB. The rest is swapped out, leading to many page faults and sluggishness when I go back to Eclipse.
Here is the preference page for the KeepResident plugin. You can adjust the minimum and maximum working set size, and enable the use of VirtualLock() to force Windows to keep more of Eclipse in memory.
Here is the memory usage of Eclipse when it is minimized AFTER installing the plugin. Notice that the physical mem usage is now up to 74MB, so Eclipse will not experience nearly as many page faults.