It's clear a pure javascript miner (like the one used at bitp.it) isn't going to be fast enough for most people's needs. I bet adding flash, java and webcl miners might make them useful.
Bitcoin Plus and Krad Miner have kept their web miners closed source, but I think the community can whip up open source replacements with a little effort. Should we start with the bitp.it miner at
https://github.com/jwhitehorn/jsMiner, or start from scratch?
I don't have the Java or WebCL chops to lead the development, but I'd love to help get a powerful web miner project off the ground.