I'm sure you've read it. It's a pretty simple document that pledges the signer to two things:
ONE, oppose any and all efforts to increase the marginal income tax rates for individuals and/or businesses; and
TWO, oppose any net reduction or elimination of deductions and credits, unless matched dollar for dollar by further reducing tax rates.
I've never quite understood why people characterize this as a pledge to Norquist. It's a non-binding statement that the signer will oppose tax increases, whether those be raises in the marginal rates or elimination of credits without matching reductions in the rates. It's really no different than simply saying the same thing at a campaign event or on the Sunday talk shows.
AFAIK, it doesn't really conflict with the Constitution in any way. If the Republicans want to limit their ability to maneuver like this, I guess that's their business. I don't much care for it, but how they do their thing is up to them. The signer can still vote however they like. They might catch hell for it, but they would also catch hell if they promised the same thing without signing any document. H-Dub learned that one the hard way.
The issue isn't some meaningless piece of paper that Norquist gets people to sign. The issue is the fiscal philosophy it represents. The pledge isn't much more than a sideshow.