I expect that, in the end, this will be one of two multi-year deals given to an arb-eligible Cub, the other being awarded Aramis Ramirez. Ramirez, to me, seems likely to follow last year's Kerry Wood path of signing a one-year deal, then reworking a multi-year deal around spring training.
Update - 7:45 PM ET Barrett's contract is 3 years, $12M. Is he worth it? That depends entirely on whether or not last year was for real. If it was, then he's a pretty big bargain. Catchers who hit .285 with 15 homers don't grow on trees, especially in Wrigleyville. His good contact rate (86%) and power numbers might indicate that he can keep it up.
The downside isn't so bad, either. $4M a year is a pretty manageable risk, especially for a team with the Cubs' payroll. There really isn't much to complain about with this deal, is there?