In that case, hell yeah, go for it. Great deal. 105 is a great group, and the Roubaix frame is a great frame. I've got an '07 Roubaix LTD, and it's really just a great bike. Moreover, under $1000 for a 105-equipped bike is a great deal in today's market (due to the dollar's decline, bike specs have dropped slightly for the $$$ for 2008 bikes).

The only thing you may consider upgrading immediately are the wheels, especially as a bigger guy, but even then, I'd wait until they start breaking spokes before throwing cash at the problem. I had Alex wheels on a Specialized before I got my Fuji, and they lasted me four years before I had any problems, even with a riding weight between 190 and 200 lbs.