Never been, but always been tempted. Sounds a bit like something I'd like but tickets are always incredibly expensive and the musical line ups are always lacklustre (this year being no exception http://www.secretgardenparty.com/lineup.php).
So is it worth it? This is the impression that I get:
1. Art-school students / Nathan Barleys doing zany things like riding a trolley whilst wearing a cape.
2. Massive amounts of drug taking.
3. Bands being the sorts that are much better live than on recording.
£180 though! Have volunteered as it'd be worth doing the worky bits for that price. Also they are fools for never booking Neon Highwire.
I made this playlist to see if any of the names I don't recognise turn out to be gems: http://open.spotify.com/user/ma0sm/playlist/71RPS0S12DIW2QUCVPVscs