According to 82games.com, Kidd led the league in plus/minus in clutch situations (defined as "4th quarter or overtime, less than 5 minutes left, neither team ahead by more than 5 points") in 2010-11 with +119, and ranked fourth in 2009-10 with +87 (note that LeBron James ranked first).
One stat in particular which stands out has been Kidd's three-point shooting in the clutch, at 45% over the last two seasons, as compared to 38% overall.
Kidd has certainly been a key factor in the several stirring comebacks the Mavs have pulled off in the 2011 Playoffs, and a spin of the NBA.com StatsCube shows that the Mavs have outscored their opponents by a staggering +71.1 points per 100 possessions with Jason Kidd on the floor in clutch situations.
Anecdotal examples of big plays by Kidd in the clutch are all over the place. Yes, he knocked down a huge three to put Dallas ahead 105-100 late in Game 5, but many of his clutch plays have been subtle and/or defensive ones (he's averaging 3.6 steals per minutes in playoff clutch situations), such as a deflection of a LeBron pass which ruined a Miami possession with the score 99-97 last night.