In response to a question put to the Engineering Division of the Special Libraries Association, Mike White at Queen’s University in Ontario, writes:
"For teaching and research purposes, the public patent databases are excellent resources. The quality and currency of the data is as good as the commercial sites. The patent office databases are updated weekly and most of the independent databases (FreePatentsOnline, Patent Lens, etc.) are current or no more than a week behind. My favorite is the EPO’s esp@cenet system. It’s user friendly, has tremendous content (60 million patents from 72+ jurisdictions) and an excellent classification search tool. I understand that they will be rolling out major enhancements to it sometime this fall. You might be interested in a comparison of free patent databases I posted recently on my blog."
Mike also notes that Thomson Reuters is rumored to have a powerful new patent searching database coming — for professional patent searchers.