For those not in the know, a Bug Day is a day when we, the developers, pause for a moment and take a fresh look at our bug backlog. For the larger community it's a chance to help triage bugs by sorting out which ones are still problems, or even just identifying the ones that need more information. After all, unless there's enough information in the bug to help developers reproduce what's broken, it can't be fixed. For anyone who wants to get into the development of an Eclipse project, it's also a great time to submit a patch and get feedback from the committers within the bug itself or through other avenues such as IRC. However you participate, it's a day to remember that we can't make our projects their best without the help of the community, and for the community to help us to scratch whatever has been itching at them.
As of right now, two committers have signed up to be contacts for the Web Tools Platform project, but I wouldn't rule out there being more committers before the day itself arrives, or more projects at that. As has been pointed out elsewhere, the first day is largely an experiment.
Join us, won't you?