Pruning nodes are described in the [sourcecode](http://bitcoin.stackexchange.com/a/35987/5406) thusly:  

> `-prune=<n>`: Reduce storage requirements by pruning (deleting) old blocks. This mode is incompatible with `-txindex` and `-rescan`.

I’ve watched that my node has been consistently uploading less than it has been downloading since I set it to run in pruning mode.

* What services do pruning nodes still perform?
* Do they upload blocks and transactions? 
* Can they service thin clients? 
* What can a pruning node **not** do, that a non-pruning node does?