We had tested BitWebServer and some others. They ran lighttpd, php and MySQL. The applications were useable. We tested weberp, joomla and phpmyadmin. We were able to set-up any android system as a web server, but suspect that such would not handle more than a couple of connections. We only tested under light loads and not all functionality, e.g. email.
We had no real interest in using a tablet or cell phone (they worked on cell phone with no problems) as a server.
The tests were run on Android 2.3 on Sony Xperia X10 (Android 2.3 at least 3 years ago - webERP and Joomla testing), Samsung Galaxy S3 (android 4.4.2) and Samsung Galaxy Note 8 (android 4.4.2).
We found the tools for software/web site development available on android were too cumbersome to be of much use.
None of the devices were rooted or running any customized versions of android.