Eric is more noted as a receiver than a blocker, even though he is a decent blocker. That's also one of the reasons SF used their 1st round pick this year on V. Davis. Davis is supposed to be able to do it all (Receive and block), much like Tony Gonzalez.
He's (Eric) has 32 receptions this year, and actually led the Niners in receptions in 2004. 05' was also a good year for him. The Niners were hoping to use more 2 tight end receiving sets with Eric and Vernon this week, so that's the big loss for them.