We use ucw for http://paragent.com (click on "DEMO" to see our app in action live). We actually use the older _dev branch of ucw, as we started over a year ago before the _ajax branch had really settled down. In fact, we've ended up removing much of the AJAX from the site for design reasons, and gone to a simpler page model with the latest site update. ucw has been pretty reliable. OTOH, we don't get hammered on the front end that much, so we may not be really stressing it. Most of our heavy-lifting is all on the back-end connections to the agents, where we have to maintain thousands of ssl connections. We have been very happy with our decision to go with Lisp.