Xamarin is a platform that prides itself on an attempt to make mobile cross-platform development acessible. And it fails. I've toyed with it in the hopes that it will make writing and deploying Android apps easier, but I was terribly disappointed.
It's not a write-once/deploy everywhere platform: the code you write can run on iOS/Android/WP until you start meddling with unique features. UI design still follows native format and needs to be done for each target platform separately.
For Android, there's absolutely no advantage at all:
* designing the UI is the same (Xamarin Studio is slightly better than the Eclipse plugin, but only slightly) * You replace Java with C# that uses Mono. Maybe C# is nicer than Java in some respects but the gimmicks of deployment (very buggy by the way) make it not worth the effort.
I don't see benefits. Complex apps are likely to take a performance hit over time. Development time is reduced by a variable factor (UI is still separate). You might not need native developers outright but when platform specific UI issues appear you'll still need some. Replacing Cocoa/Objective-C and Java developers with Microsoft-bred C#/.NET developers - are you up for that?