I am always looking for cheap and small micro controllers. Since I moved from 8051 and HC11 based boards three or so years ago, I have been using the Atmel based Arduinos for the most part.
For the past two years, I have used mostly the Mini Pro's in most projects. I like them due to the small size and the fact they are less than $3 USD on eBay. I would love to use Nano more, but due to cost and issues I have not. Now, I have ordered a few (5 or 6) Nanos from eBay, and have had mixed results with them in the past.
The problems have been: