To kind of expand a little, the answer somewhat depends on a few factors. At a first approximation, there are two main factors to contend with. One is as Frank mentioned, and that is parasitic capacitance per foot of the specific cable, and the other is resistance per foot (there are others but we'll leave it at those two for now). The resistance per foot will affect voltage transfer, as it will add in series with the DCR of the pickup and create a voltage divider with the input impedance of what's on the other side of the cable, which can attenuate the incoming signal depending. Thankfully most guitar oriented stuff like guitar amps, and most pedals are expecting this, and have a reasonably high input impedance so voltage transfer isn't necessarily heavily affected by this nor is the resonance frequency dampened by trying to drive a heavy load, keeping in mind this input resistance will also be in parallel with the guitar volume pot, which will lower its total value. A coil with a lower DCR will fair a little better than one with a higher DCR when it comes to voltage transfer speaking in absolutes.
The capacitance per foot, as Frank mentioned, will look to be in parallel with the pickups coil and add to the already intrinsic coil capacitance. this will have the affect of shifting the resonance frequency down as Frank mentioned, which can be good or bad.
One way you can get around these things may be to use a buffer between the pickup and the long cable, if you plan on driving long cables. You can even half ass it a little by using a unit that has one in bypass mode as well, like a ts9 and plugging into it with a reasonable length of cable, and then have the ts9 drive the longer cable, you would be a bit on a leash with that method though unless you could clip the thing to your person somehow. If you were crafty you could certainly build a clip on buffer for the cost of a few pennies and a battery.
Hope this helps.
Edit: or better yet just build the damn thing in an altoids box.
