ServiceStack is just plain awesome when it comes to developing web services, though it's gone commercial for v4 onward. Nancy is another popular alternative - it's basically Sinatra for .Net. Every time I go back to WCF I want to stab myself in the face.
I've attended several and I'm a .NET developer too. You'll be safe. Yes there's loads of Ruby and Node devs there but in the main people aren't prejudice. My experience is that it's more about ideas and not about language implementations.
Ideally you could specify an HTML element to place the notification near, and then pass whatever element the user activated to trigger the notification. Or you could specify target coordinates, and compute the desired location yourself. Both of those ought to use optional parameters, though; defaulting to center seems reasonable.
If you look on the demo page (http://fabien-d.github.com/alertify.js/), all of the alerts get injected into #alertifylogs.alertify-logs which is positioned by css and therefore should be easy to overwrite: