Solaris 10 adds a really neat tool called DTrace. I wasn’t impressed at first, but I finally sat down and read a detailed explanation of the tool. It is very cool. Basically, DTrace allows you to stick a debugger on any process running on a Solaris box without impacting performance. It is a great feature, and I wish it were present in Windows. There are definitely times when we attempt to track down application stalls or excessive memory leaks; this kind of tool would allow us to pinpoint exactly what was causing the problem.
Bryan Cantrill from Sun wrote up an excellent description of using DTrace on his blog, The Observation Deck. I recommend reading the entire entry. It will take a while to work through the entire article, but it is fascinating.