I added a bright cap (aka "treble bleed") to my Les Paul and I love it! I always hated how the tone got muffled and lost clarity when rolling off the volume pot and this has fixed it. I can finally play a clear clean sound and overdrive tones just by using the guitar volume pot! I used a 0.001uF (1000pF) ceramic disc cap. It's the best $0.35 I've spent in a long time.
I plan on doing this to my strats also but may have to add a resistor in series with the cap to keep it from being too bright.
More info: http://www.bothner.co.za/articles/volumepot2.shtml
Thanks to paulster for sharing the link.