Nick met us on Facebook, and told us of recently upgrading his old Zipp 404 to 11s, only to have the driveside flange break soon after. This is a really common fault with this generation of Zipp wheel. The alloy used in the hub, it's design, and the radial lacing pattern on the driveside all act to accelerate fatigue in the flange. If it hasn't yet happened to your wheel, it's a matter of time. Sorry.
We recommended replacing the Zipp 188 hub with an XLR8 MD. These are light, strong and an economical choice. Parts are readily available through us, and they use great quality bearings, and an "anti bite" freewheel insert to stop the cassette gouging the splines of the freehub. All one needs in a hub really. We relaced the wheel with Sapim Race double butted black spokes, and black brass nipples.
Get in contact if your Zipp's need some love.