While it is way too early to be talking about renewal for next season, it's not too early to be thinking about additional episodes for this season.
You've got to think Chuck performed pretty much as NBC expected it to. If anything, NBC brass is probably relieved that it lived up to expectations against. While I normally am not a fan of the notion of "skew", preferring much more to deal with absolute numbers, Chuck's male skew ahead of The Event likely bodes very favorably for additional episodes of Chuck.
Last season Bill did some analysis on gender skew on scripted shows, and Chuck was the most male-skewing live action scripted show trailing only Fox's animated series. That works well for NBC in terms of The Event, which came in second, a 10th of a point behind CBS with men 18-49, and won (at least on broadcast, surely did better) with men 18-34 between 9pm-10pm. So even if NBC stuck something else on at 8pm that rated about the same as Chuck, if it fewer male viewers, that might not benefit The Event as much.
Of course if The Event tanks in the next few weeks, that will be moot, but otherwise I'd expect Chuck to wind up with 19 episodes, just like last season. The only way it seems likely Chuck would get a full back nine is if other new shows quickly tank and additional scheduling spackle is needed.