That bright cap should have no effect when the volume control is maxed, and is used to boost the highs at the lower settings. While Tele's often used a 0.001uF cap I like the more subtle effect of a 180pF cap across a ~500k pot (which is supposed to be what PRS uses a lot- I found that out afterwards). And I just heard from someone using a 120pf. While the value of the cap effects the frequency, it also seems to effect the relative volume of the boosted signal to the "normal" signal. So by using a smaller valued cap, it seems to make the overall signal at the lower settings less bright rather than more bright.

    There seem to be two schools of thought on the bright cap. With the tele, I guess the idea is to allow for a brighter clean sound when you back off the volume control. But I like the idea of a balanced sound that is has roughly the same tonal balance as you back off the volume control, hence the 180pF cap (I usually use mica caps for this).

    The tone pot and tone cap will have quite an effect on the sound, even with the tone control maxed. You can hear this best if you use a switch to bypass the tone control, which makes the signal louder and brighter. A larger cap produces bassier sounds at all settings, while a smaller cap produces relatively brighter sounds. The EC "woman" cap is reputedly a 0.015uF/630v cap used with a humbucker and gets that smooth sound from when he was with Cream; you can turn it all of the way down and still have some definition.

Try experimenting with a resistor (try different values) in series with the treble bleed cap, placing the series RC combination across hot & wiper terminals. This will tend to soften the boost. It's sometimes hard to get just the right cap by itself to do the job. A resistor can help you tune the control for a more pleasing overall useful range. 

i've had pretty good luck with the following:

for the vol pot cap i use the formula 1 pf / ohm on the pot. so, on my strats, i'm using 220pf for the 250k pot... on my humbucker strat i'm using a 470pf.

for the tone control i went pretty extreme.

i think a lot of guitars come stock with either a .05 (single coil) or .02 (humbucker).

i started experimenting and ended up using .0047 on all my guitars.

what this does is accentuate more of the midrange the farther you turn the tone down. in fact with the tone on zero and a decent amount of distortion, i can get a good boxy honkin' tone happening. for me, i've found this mod quite useful. with a good blues OD/tubescreamer type setting on a Fender BF/SF amp and the tone to zero on the guitar, i can coax some good tweedish tones out of it... just by using the tone control only!... very nice. 

before, everything sounded like mud if i turn the tone below 8. lately though i've been think of bumping it back up to a .01

shoot, maybe i'll install a p-p pot on the tone control to switch between .0047 and .01 hmmm

YMMV

one other thing... if you want to "experiment" with different values of caps, just hook up a couple of alligator clip leads to the contact points on the volume and/or tone pots and let them hang out the bottom of your pickguard (if you have a strat or tele style guitar... no problem on a LP)... and switch different values in and out until you find some that you like.

As has been discussed here, though, the cap value *will* matter and needs to "married" to the pickup and pot value. If you are using single coil pickups and a 500k volume pot, chances are you're getting a pretty strident tone at full volume anyways. Sticking in a bypass cap will only exaggerate that as you turn down. Some players describe it as a "brittle" tone.

There are several fixes, some of which were posted by others earlier. I'll summarize and expand where needed:
1) Change from a higher value (500k) to lower value (250K) volume pot for the relevant control(s). This will sweeten things a bit by losing some of the high end altogether.
2) Keep your current pots and bypass cap but stick a small value cap (e.g., 470pf) between hot and ground on the pot (the two outside lugs) to take some of the harshness or edge off. This will work independent of volume settings.
3) Use a smaller value bypass cap, such as 470pf, so that stuff which your speakers are not so great/efficient at reproducing is the lion's share of what is retained as you turn down.
4) Use the bypass cap currently installed, but stick a resistor in series between the cap and the wiper of the volume pot. What this will do is effectively create two different "volume pots", one for the entire signal and the other for just the high end. The latter is a divider made of the added resistor, and the resistance from the wiper to ground. A resistor of about maybe 1/4 to 1/3 the value of the pot itself might be a good place to start (e.g., 120k). 
Incidentally, this (#4) is what the Fender Custom Shop has used. I had the particulars in a note John Suhr sent to me some years back, but I'll be damned if I know where it is. The principle remains the same, and the values are probably best selected for your guitar and tastes. What I *will* point out is that with a series resistor installed, one has much more latitude with respect to choice of cap value, since the impact of the cap can be toned down a bit, simply by raising the resistor value. Larger cap values (e.g., 1500pf) let one use a compensated volume control as a kind of ersatz "bucker-to-Fender" control with dual-coil or bass-heavy bridge pickups, since they retain much more of the midrange as the volume gets turned down to about 7 or 8. After that, they tend to sound like regular volume controls.

As an aside, the bypass cap was intended to offset two phenomena: the loss of high end due to impedance issues, and the loss of high and low end in our hearing as the signal level declines (the famous Fletcher-Munson curves). The "loudness" switch on your stereo does the same thing only the active design of the stereo amp allows it to boost both very and high frequencies as the volume gets turned down...like its supposed to. See, now you've gotten me curious about use of a dual-ganged volume control and more complex circuitry to compensate volume for human hearing. 

Steve, if you really want the classic blues and rock tone, skip the humbuckers altogether. Get a set of Rio Grande Bastards. They are P-90 single coils that are a form and fit replacement for humbuckers. Be sure to keep the originals for resell time!!