All Gibsons, perhaps one or two other US companies, and almost all imports use linear volumes. I prefer linear for clean, as it's smoother taper from about 10-2, with a more rapid roll off from 2-0. They work great for things like Jazz bass or LP because you actually get an even fade out of one pickup across a wider range of the turn, and doesn't kill the overall volume on a LP middle position until you get to the very bottom.
Audio has a more rapid roll off in the top third of range, less effect in the middle third, and more again in the bottom third, though with a smoother shut down at the end than linear. Most players prefer audio, as it offers a nice quick clean up from overdrive when you knock it back to 7, and which point you have that big flatter area in the middle third to land on without having to be too precise. Then it offers smoother swells on fade ins and outs.
In theory, linear should not be useful for volume, and linear should act as Bob said, but in a guitar circuit the results don't often work that way. After putting the pickup/generator to one side and ground on the other, other pots, caps, amp input impedance, cables, etc., the end effect doesn't really follow the logical curve. What I'm describing is what is heard, not how it looks on a chart.
i just switched out the stock linear pots on my vos lp special with audio taper and couldn't be happier. to me, there was basically no adjustment using the linear taper pots whereas now i can actually use the controls. but as with anything, ymmv!
I'm a linear man though I can see the use of audio in some situations such as going from WAO to fairly clean in just a few positions, 6 or 7 on the knob maybe. Linear is better for making small changes in volume until about 2 or 3.
to distill DC's informative comments, use linear taper volumes if you play bass or completely clean guitar, and use audio tapers if you use any kind of gain or compression. use audio tapers for tone in either case.
if you're big on tweaking the blend of two pickups on a les paul and not so worried about how the individual pickups clean up with gain, you might like linear volumes.