As every developer should know m the SPSite and SPWeb objects have problem resulting in memory leaks. On the background they call “unmanaged code”. so when using SPSite objects or SPWeb objects in your code, always use ways to dispose these object (think of try-catch and using).
there is even a tool to check if you really dispose all the necessary object (link)
But today i saw an article that told me there is another memory leak problem.
Look at this article of Todd Carter to see more of it, he call’s it : SharePoint’s Sasquatch Memory Leak