Although SharePoint 3.0/ 2007 (MOSS and WSS) is built on top of ASP.NET 2.0, there are still connection to unmanaged COM+ codes inside. Whenever you programmably playing around with SharePoint APIs, remember to dispose the SharePoint object instance.

Roger Lamb’s blog post here has very details explanation on this subject even it has been mentioned again and again before.

http://blogs.msdn.com/rogerla/archive/2008/02/12/sharepoint-2007-and-wss-3-0-dispose-patterns-by-example.aspx