Never heard of them, but your description made me curious enough to check out the website. The website allows you to search for "partners" (i.e., bike retailers who will accept the Commuter Check vouchers) in your area. Check it out here: http://www.commutercheck.com/Partners/PartnerList.aspx

Seems like a lot of hassle to avoid paying a small portion of payroll taxes, if you ask me.