Lluis checked-in last week a new memory profiler for Mono applications.
He originally created this profiler based on `heap-buddy', while trying to understand memory consumption in MonoDevelop. I used it last week to trim down 340k of Tomboy memory consumption (removed a Hashtable that contained bools).
If you are a Mono application developer, you will find this tool very helpful in finding where your memory is going. It will look your app look better (and Mono look better ;-)
For more information see Lluis' Blog