I've always liked him (I'm a 9er fan as well as a Lion fan). He's always been solid-above average IMO.
The bad news is he really strugled last year and is almost definatly in the decline of his career. But to be fair, if the rest of SF's line hadn't been so god awful Gragg could very well have been a solid player last season. I think he'd add excellent depth to Detroits Oline and may still be capable of being a solid starter for a while longer. He's not worth anything near the $3 mil he was going to cost the 9ers though.
I'm still a little worried about Detroits Oline this season. If he doesn't demand a huge contract (I can't see how he would at this point) I'd like to see him playing for the Lions.