Ooh, what is THAT? You totally piqued my interest. I suspect I'll be arriving too late to enjoy though [[won't be in town until around dinner time) but I love bike tours! I already have a Wheelhouse tour booked for Sunday, but if I could I'd bike all weekend long.
Critical Mass doesn't usually start until pretty late, but you'd have to get a bike in time. I think it is a blast, so if you like biking I'd strongly recommend it. It lasts a while, so you might be able to join late if you can find it. That might be too hard for a visitor. I won't be there, but maybe someone else could help.

http://www.facebook.com/group.php?gid=15776293209 You should check the page because they change the times and locations sometimes--the page says 5:30 at Grand Circus but that isn't always the case.