Microsoft has just announced that they are open sourcing ASP.NET Web API and ASP.NET Web Pages (aka Razor), to join the already open sourced ASP.NET MVC. These will still be included in releases of Visual Studio and have full time development staff working on them but they will also take in 3rd party contributions.
It's not technology I've looked at other than ASP.NET Winforms (the original) which is ok, but my preference is for the non Microsoft PHP. Recently though Microsoft have embraced open source and now make extensive use of jQuery, jQuery UI, jQuery Mobile, jQuery Validation, Modernizr.js, NuGet, Knockout.js and JSON.NET which is about as up to date on the client side as it gets.
I can see myself coming round to ASP.NET MVC though I'm still hedging my bets with PHP for server side web development as it works on both Windows Server and Linux. So maybe I'll return to ASP.NET (I prefer the C# language to PHP- confusing eh!) in the future for tutorials etc.