I have no idea when (I fully expect them to) Twitter will bring back a complete profile search, but I've been in the process of creating my own for about the past month or so. I've recently added some additional XML and JSON output to enable programmatic access if other developers are interested. It's called TweepSearch (http:// tweepsearch.com) and searches about 1.8m Twitter profiles right now including username, screen name, bio, location and url. I'm also planning on adding geo-based support at some point.
A quick (and most definitely dirty) example of using JSON to integrate search results can be seen on my blog at http://dcortesi.com/2009/04/07/twitter-profile-search-api/ If you're interested in using this, please contact me so I can a) be aware and make sure I know who to notify if I make a change and b) what kind of traffic I might be able to expect. For the time being, I'm providing this as a free service until it becomes overwhelming or Twitter releases their own. ;) I look forward to hearing your feedback. Thanks, dpc p.s. An additional thing I set up recently is http://twitteravatar.appspot.com - for when you need programmatic access to a Twitter avatar. I'm familiar with SPIURL, but that seemed like more of a library than something intended to be heavily used.
