IIS and Threads

We are starting to write more and more code for an ASP.Net web application uses a new thread to complete long running tasks. I can find no solid documentation that give any useful guide to any limitations of restrictions of using threads within IIS (6). Any advice to this end would be appreciated - specifically the following: - What (if any) is the max number of threads - Is there a recommended max number - Are there any pitfalls of using threads within an ASP.Net IIS web application? Thanks for any advice