As it turned out, Hill was the least productive of the original five, but is the only one with an assured job going into 2011. Gonzalez' hot start was shrewdly flipped for Yunel Escobar, Buck and Overbay are free agents, and Encarnación is a non-tender candidate - though my guess is he's your 2011 starting third baseman.
This is a 2010 review post, though, not a 2011 outlook, so let's look at how everyone performed this year, and let's do it with a colourful table, because I'm just gonna tell you the stats anyway. Might as well get it all out of the way at once! Also included besides the previously mentioned guys are Jose Molina, John McDonald, and Adam Lind.
So the infield, aside from tiny contributions from guys like Mike McCoy, Randy Ruiz, and Nick Green (remember that?) contributed 13.4 of the team's 42.3 WAR (aside: I suppose this means a replacement-level team would win about 43 games, just FYI). I have no idea what percentage infielders usually account for, but I'm guessing it's higher than the Jays' 32%.
There isn't much left to be said about Buck and Gonzalez: both signings worked out very well. Gonzalez became a young shortstop with upside and a track record (not literally, of course), while Buck handled a young pitching staff with aplomb, made the all-star team, and will net the Jays a draft pick when he leaves.
Overbay had a solid Overbay-like season, and if it was his last a Jay, I'll be sad to see him go. In five seasons with the Jays, he was an above-average hitter every season except 2007, and a very good fielder to boot. But he's 33, doesn't exactly have an "athletic" build, and struck out more times this year than he ever has.
As much as we like to pile on E5 'round here, he didn't have a bad year. He was an above-average hitter despite a .235 BABIP and was actually close to average in the field. (Fangraph's breakdown of Edwin's defensive stats claim that he has above average range, but makes too many errors.) I wouldn't mind the Jays bringing some competition to spring training, like Brad Emaus, but I also wouldn't mind Edwin Encarnción: 2011 Starting Third Baseman.
I've been through Aaron Hill's season before. It was really, really weird. If you don't feel like reading through the entire afore-linked article: Hill was the victim of an absurdly-low BABIP, but he also changed his approach to one that should produce lower BABIPs, but not nearly to the extent it did this year. I think Hill will be fine - regardless of whether he goes back to hitting line drives at a 20% clip like in 2009 or maintains his 2010 uppercut, he should be an above-average hitter, and combined with his defense and position, that makes him an asset.
Adam Lind I'm not too sure about (I've been through him too). His season was just as bad as Hill's (much worse when you consider he's a DH not adding any value with the glove), and his component stats suggest he wasn't unlucky; he was just awful. At this point he looks like a platoon bat to me.
The big acquisition of the season was Yunel Escobar. Escobar played pretty well after arriving, though not quite at his 2009 level in which he put up an excellent 4.3 WAR. Escobar posted the worst power numbers of his career, which can partially be explained by his career-low 3.3% HR/FB. Hopefully we'll see a regression to the mean next year.
I said at the top that the 2009 infield looked like an uninspiring bunch. I can't say that's changed too much; there's more "upside", whatever that means, with Escobar, Hill and Arencibia, but Escobar and Arencibia's upsides might just be what Gonzalez and Buck did this year. At least the middle infield is locked down for the next few years, and if Arencibia performs as his AAA numbers suggest he can, the entire up-the-middle part of the infield is stable, and that's a pretty good start to building a contender, even if none of those guys are superstars.
And that about wraps up the 2010 Infield Review. Johnny Mac and Jose Molina had very nice seasons off the bench, and will presumably still be on that bench next year.