You can find in this thread
http://forums.sgusucks.com/showthread.php?581-David-Hewlett-News-and-Info
already some news from David Hewlett and tweets he got after he wrote this on twitter:
There are also more information about the episode they are in in the Season 2 SPOILERS thread:
http://forums.sgusucks.com/showthread.php?386-SPOILERS-Season-two
And there is now an article about David Hewlett and his opinion about the SGA/SGU crossover on Gateworld:
http://www.gateworld.net/news/2010/09/hewlett-discusses-sgasgu-crossover/#comment-12582
I already knew they were going to destroy my second favorite SGA character (McKay is second, Sheppard is my first, Teyla is my third, Ronan 4th). Woolsey doesnt make my list of SGA characters, and I personally dont even count him in because he just didnt click in SGA for me.
In that interview, Hewlitt says they "let just enough of the character in, but not enough to take away from SGU". To me that translates into "pod-McKay, not OUR McKay". Just like Daniel and Jack. Only Amanda Tapping was able to come into SGU and convey a quiet smugness like "hahaha...im here, but Im sooo not into this cheesy cameo".
Do they really think the fans will come back in droves to see that episode? NOT!