What books / resources did people find helpful on .Net?
The best resource for me is Joe Duffy's blog . He (I would say) is the largest expert on .NET concurrency issues, as well as the lead developer and architect of Parallel Extensions to.NET.
I think you will find useful column " Effective parallelism " Herb Sutter
Joe Duffy has a book that has been praised: concurrent programming on Windows .
Parallel FX Team Blog . Hands down is the most useful resource for programming parallelization on .NET (at least if you are focusing on that soon).
Daniel Mot's blog also contains a lot of useful information.