Thinking of using Xamarin for the development of a mobile app for a side project. Yea or nay? Android and iPhone.

I love it. Maybe not Xamarin Forms depending on what the app is but Xamarin is great!

@ridecar2 out of curiosity, why not forms?

Forms is great if you need navigational master detail data entry app. Also it works on 99% of devices. If you need something more advanced, platform oriented i still prefer xamarin cause you have bouth projects in same solution, and can use same nugets. Minus is ... there are more examples and help for native platforms online.

Xamarin Native is fine, I personally wouldn't touch forms. Sure it's faster to develop but only for easy apps. As soon as you want to do some platform specific things you're better off with Xamarin native (+ in the long run for personal development I believe it's the better choice).

After using Xamarin for a while though I have to say the build times really get on my nerves + Xamarin Studio has a lot of random shit going on so prepare for several restarts and IDE difficulties.

All in all I'd still recommend it though if you're into C#. The code reuse is great.