I think that this would have to be one of the most time consuming and complicated tools I have looked at so far. It takes a large amount of time to try and create a learning objects, that often looks vastly different to how you intended. I don't think that I would ever attempt to use this as a learning tool as the more traditional approach suits my style much better.
The time that it takes to prepare a WebQuest is phenomenal! I don't think that enough of the curriculum could be addressed to make it an effective tool to use. Unless one WebQuest could be used for 5 or 6 classes, or recycled for multiple years, the time imput factor is to great to want to created this learning tool.
I don't like WebQuest, I don't think that I could use it, and I don't think that I ever will.