After two games? Let's let the guy settle in before we make any judgements. He looks real good so far, and is likely to get better.
The dilemma, IMO, is that, assuming Smart continues to get better, we'd now have two starter-quality guys playing the same position with roughly similar skill sets (defense, pass-first approach). The 3-guard lineup, while intriguing, won't work for a lot of opponents. Meanwhile, down there under the basket, there's no real classic 7-footer (KO's becoming a very good player, but he's not a banger).
If a quality true Center comes up, do you trade Rondo or Smart for him? Given that Rondo's going to be commanding a pretty hefty paycheck soon, the smart business move might be to trade him and hand the keys to Marcus.