My instruments are mostly used and cheap, and I'd gotten used to cursing them fairly frequently for valves sticking, slides moving only grudgingly, and so on. I'd also thought about cleaning them, but figured the cleaning I'd already done on the valves and slides meant that a cleaning wouldn't make a big difference in those areas.
A week or so ago I got a very used slide trombone. It'll be fine for my own entertainment, if not a professional instrument - but the slide was very very slow. A friend who plays trombone thought the slide would benefit from a cleaning, so that finally triggered my cleaning all my used instruments - a trumpet, valve trombone (with valves that would restick within half an hour of lubrication) and the slide trombone. It made for quite a shiny pile of parts:
(bigger image at http://simonstl.com/pics/disassembledBrassB.jpg)
Apart from the fun of disassembling and reassembling and watching clouds of dirt emerge from the brass after snaking it, I'm very very pleased to report that the valves on both the trumpet and the valve trombone are much much much smoother, and haven't stuck since the cleaning. They'll get there eventually, I'm sure - there are horizontal scratches on the trombone valves just waiting to catch on to something - but for now, wow! I never thought these instruments would play like this.
The Yamaha Brass Soap I used was a pretty cheap ingredient for this kind of improvement. (I suspect it was more the fact of cleaning than the specific soap.)
The slide trombone moves better, though it's still a fairly slow slide. Since I don't plan to do anything wild with it, it'll be fine for me, I expect.
If you haven't cleaned in a while, definitely give it a shot!