It's quite clear that Frank Gore's best years are behind him, but some of the thoughts people have on Frank Gore is that he's done. They think this is probably his last year to be a feature runningback and quite possibly his last year on the team.
In watching him the last few seasons, it's difficult to say how good he is. A runningback is very much the product of his offensive line, and the line just hasn't been too good up until last season. His second season, 2006, was his most productive year when he nearly rushed for 1600 yards. You have to remember that we had a very good run-blocking line (Jonas Jennings and Larry Allen manned the left side), Norv Turner was our offensive coordinator, and Antonio Bryant was doing a very good job serving as a deep threat. 2006's offense was very conducive to running the ball. In subsequent seasons however, like Alex Smith, Frank Gore in the running game has been pretty hampered by multiple offensive coordinators.
Last season, he started off slow and it really did look like he was done... but then he went on a tear mid-season in which he had multiple 100-yard games. He was well-rested by the coaching staff as well, so I'm sure that prolonged his life as a runningback. However, I'll say that at times he didn't seem to run as hard as he used to when he was in his *best* years. The Frank Gore I loved to watch would keep his feet churning and explode for an extra 2 yards, even when it seemed like he was stopped. He still runs hard, but there are times when he just goes to the ground. I don't know if coaches have been having him go down to prevent wear and tear, or if he just doesn't have the explosive ability, or if it's just a matter of minor injuries effecting him.
Even so... I think Frank Gore is a great asset to our team, and even if he isn't capable of 250+ carries anymore, I hope he sticks with the team for awhile, and we have a very strong runningback-by-committee. It'd be a shame for him to be THE offense for so many years and no longer be a productive player when this team is ready for a few pushes at a Super Bowl run.