Mike,
I raced 404's as my go-to road wheels for a couple of seasons. They're great wheels and for the most part I loved them. Unlike Dietmar, I had some scary experiences when riding fast in gusty crosswind situations with a 404 up front, especially in fast moving echelons during races. But that was riding and racing in Utah and Wyoming which can be pretty windy places. I eventually sold the front, relegated the 404 rear to my TT bike with a cover and went to American Classic 420s as my race wheels. I see lots of folks racing 404s out here near Seattle but we don't get the same kind of windy conditions here.
The 404s are pretty expensive and not terribly light if that's important to you but I generally didn't ride them in crits after watching too many riders destroy thousand dollar carbon wheels while contesting a pizza prime.
In terms of value, you can do a lot better than Zipp wheels, they're fine wheels but they get a premium for that name. Check out a good local wheelbuilder or check out some of the offerings by:
(Neuvation)Wheels
Welcome to Williams Cycling
american classic - ROAD WHEELS
or others for decent deals. A lot of those wheels are actually built on Zipp rims.
BTW, I love my American Classic 420s and have no qualms racing them in heavy winds or even crits as they're fairly tough and not too expensive to replace. I also really like Kinlin rims, DT Swiss 1.2s, and have a Neuvation wheel on my cyclocross bike that I'm real happy with.
I like Zipps just fine, but there are better values out there including most custom built wheels which are less expensive than many folks realize and personally I wouldn't ride day to day on my 404s nor crits but that's just me.
Good luck,
-Dave