Without specifically endorsing any of the following there are other blogs that I know it frequently discuss OPC. Well I guess I will endorse one or two of them..
Included in the list are
http://radio.weblogs.com/0133292/
This blog is is written by Gary Mintchell. Gary and I have known each other longer than we both care to remember. Gary and I both come from Ohio although we are on opposite ends of the state. You can count on Gary to provide you the most useful information via his blog, and he has an extensive portfolio of articles that he is written on just about every topic. Regular readership of this blog is a must for anyone in automation.
http://msmvps.com/blogs/opcfr/default.aspx
This blog is the ramblings and information from my French colleague Michel Condemine.
Michel is a dedicated evangelist for the OPC Foundation. Him and I regularly communicate via messenger and every so often we manage to connect up in the same city.
http://www.opcofamerica.org/events/articles/060205_blogs.php
although this particular blog is a little outside of the OPC in automation spectrum but I felt it was humorous enough that you might find it interesting.
http://blog.matrikonopc.com/
This blog is written from my good friend Eric Murphy, and I highly encourage regular readership, as he is very entertaining and at the same time has a lot of good factual information that can benefit both vendors and end users alike.
http://us.profibus.com/community/blogs/pto_profiblog/default.aspx
This blog is written from my good buddy Carl Henning, and again I highly encourage regular readership, to really get a good picture on the industrial ethernet and specifically everything associated with PROFI..... Carl also been associated with OPC in very many ways, and I had the pleasure to have lots of enlightening discussions with him about everything under the sun, and of course there's lots of sun in his new hometown Scottsdale, Arizona. He is a wealth of information, and definitely deserves regular readership.
I also encourage regular visits to http://www.opcconnect.com/ .
Mike is a wealth of knowledge and is a must reference for any developer or anything associated with OPC. Mike is an excellent adversary for me with respect to his opinions, and I always welcome the e-mail dialogue dialogue that Mike and I have on occasion.