The club rafted Butler's in Feb. 2001, when it heard that this normally Hydro diverted (i.e. always dry) river was running as the lack of water in other dams led them to use the butlers gorge turbines for generation.
There are two sections, a continuous G5+ section, and a continuous G4+ section. The G5+ section is extremely narrow and very steep and is thus nearly impossible to raft. The G4+ section is much the same, but slightly easier - so we rafted it.
The top section has some powerful waterfalls, the lower section is half as steep without the waterfalls. and flattens out at the end.
Butler's is about the most difficult river you could raft in Tassy, and makes for a continuous adrenalin fix. Oh, and it also goes through some nice forest too.