I use an Alfine 8 on a fully rigid Trek Sawyer 29er as my ‘winter bike’, it gets the full local trails treatment through all sorts of crap conditions and keeps rolling. It does a few jumps off logs and stumps etc but nothing bike-park like and you’ll not be throwing in any whips! The back end does feel heavy because it is (particulaly on my steel framed monster!). The feel of the bike is of the get anywhere but not in a particilaty sprightly way variety.
It has been very good reliability wise and the gears get me up everything I’ve pointed it at. I’ve given the Alfine an oil bath to keep it running sweet.
I do like it, but on sunny days invariably choose a more fun bike to ride. Remember to carry a rear wheel spanner in your pack as it’s a right pain readying a new tube to fit and staring blankly at the rear wheel nuts :-/
Andy