I went from a 15/39 to a 15/41 which is a slightly smaller change than going to a 14/39.
I prefer sticking with the 15T up front because the smaller radius of a 14T can potentially accelerate chain wear and wear on the slider on top of the swing arm. Opinions are divided on this issue, but I tend to go with the conservative side to minimize the potential for wear.
Either way, I don't think you'll see a significant drop in fuel economy or top speed. This has been discussed well in other threads so I'll just go with the short version: If the stock gearing doesn't allow a specific individual bike to reach it's peak hp rpm in top gear, going to a lower gearing may actually increase top speed. It depends on the state of tune for that particular bike. In reality top speed will probably remain very nearly the same. Driveability at lower speeds will definitely improve as many folks have attested to.
I went from a 15-39 combo to a 15-41 for the same reasons as Mark1305. I think I may try a 42, just cause I'm bored.
I still get 40mpg. ;D
Check to see if you have enough chain for a larger rear sprocket, as I had to add links to go up 2 teeth!
I'm assuming you have the stock gearing of 15-39. Go ahead and buy the 14 and install it. You'll be very happy with the results. I ran 15-41 until I wore out my first chain (5% drop in gearing), then went with 14-39 after that (7% overall). I consider the gearing to be just right with either of those two setups.
The 14-tooth front was only about $20.00 from the local dealer. Just do it.
If I were better at proofreading I wouldn't have to go back and fix spelling mistakes. :-[
You can change the front sprocket without putting the bike on a stand. To change the rear, you have to remove the whole rear wheel first. I've done a rear but not a front, so I have no firsthand experience in how much easier a front is than a rear.