I don't think we'll ever use Velcro again. In '06 and '07 we used velcro, and replacement was just a hassle sometimes since the velcro backing doesn't always like to separate from the velcro...and as previously suggested alot of times our velcro sides didn't match up.
In 2008, we used #8 and #10 nylon screws. With nylon screws you can drill a hole, hot glue the nut in place on one side, and effectively have the equivalent of a tapped hole. For 2009, we'll probably use rubber-backed washers with steel nuts & bolts for the cRio, and varying sizes of phillips-head nylon bolts for the rest. All will be mounted on honeycomb fiberglass that will have a nice glossy finish put on it in the end.
For the cRIO & PDB, think about the risk vs reward. You'll save a few ounces at the risk of an imperfect <adhesive> connection coming loose. Should the risk come to fruition, the consequence is that you may have to replace a several thousand dollar part that you're supposed to also use in future years' FRC competitions...not just 2009. Is it really worth the risk?