maple fretboards give a brighter sound. it's...spanky, for lack of a better term. i'd describe them as having more attack than a rosewood fretboard. of course, this is all variable because it depends on a lot of different factors from the curing of the wood to the velocity at which sound is transmitted through the wood, to the wood's density. even woods within the same family can have different tonal characteristics. for example, Brazillian rosewood is pretty bright-sounding, while Indian rosewood is warm.
if you can't tell the difference, i suggest putting a rosewood-fretboard strat side by side with a maple-fretboard strat, blindfold yourself, and play each one unplugged. the difference is audible by most people and obvious to those with sharp ears. this difference is also audible when plugged into a good amp, because the function of good amps is to impart a guitar's tonal characteristics with minimal coloring.
in fact, even with high gain the woods you choose for your guitar influence your final sound. if you had a mahogany-bodied les paul with humbuckers and an indian rosewood fretboard, going through 2 12-inch speakers, vs a mahogany-bodied les paul with a maple cap, soapbar pickups, and a brazillian rosewood fretboard going through 4 10-inch speakers, you'll find the first one to have deeper bass response but possibly sound a little bit muddy, and the second one to have a tighter sound with less bass and more midrange - even if you use a tight high-gain amp like a VHT pitbull.
everything adds up to an audible difference.
