The latest release of the Spring Tool Suite (3.2.0) contains a large number of performance improvements in many different areas. We are not only adopting the latest improvements from the Eclipse Juno SR2 maintenance release (which fixes a large number of performance issues with the new Eclipse 4 platform UI), we also worked on the performance of many of the STS internals, specifically targeting Java editing and build times for Spring projects.
To demonstrate the improvements, here is a quick screencast showing STS 3.1.0 and 3.2.0 side-by-side:
There is still more to do and we will continue to work on these areas for the STS 3.3.0 release, scheduled to arrive in July 2013. If you want to know more details, watch for further improvements, submit additional information, and/or report specific performance or memory issues, please watch/use this JIRA ticket: https://issuetracker.springsource.com/browse/STS-3054. Throughout the STS 3.3.0 development cycle the usual nightly and milestone builds will be available if you want to try out the very latest improvements - feedback welcome!