I've yet to read a patent that actually contains useful information. I'm sure they're out there, but generally they seem to be written in as obfuscated and generic way as possible, as their sole purpose is to enable litigation.
You might be safe with reading expired patents, but don't take my word for it. I do sometimes and get a kick out of it. Where would we be without a patent for a "Baseball cap for pigtail hairstyles"? http://www.latepatents.net/5799334.htm (Their site seems to be dead in places, but you can still browse through a few of them with google https://www.google.com/search?q=site:latepatents.net )
Academic papers at Arxiv and elsewhere are far more useful.
