Carlos Boozer is a defensive liability in man-to-man situations + help defense at both big man positions. He is less of a liability in man-to-man situations at center than at power forward.
However, playing alongside a player like Zach Randolph, Boozer's defensive weaknesses (as well as Randolph's) will be even easier to exploit. Both are weak defensive players who lack quickness / mobility / height / length. They'll be the comparable to (defensively) the Kevin Love + Al Jefferson combination on the Timberwolves.
Boozer at center alongside a player like Lamar Odom or Kevin Garnett wouldn't be an issue.
One thing people are overlooking is that Dampier is the starter. When Boozer and Randolph are in the game together, it's either going to be against teams with weak frontlines, or against teams' bench players.
The question to be determined during the season is which big gets minutes with Randolph if both Dampier and Boozer are out of the game. Right now, the plan is to go with Drew Gooden for 8 minutes or so per game, thinking that what he lacks in defense, he'll make up in offense and rebounding (again, especially again second string players).
However, the more I think about it, the more I like Petro as the team's backup center, in front of Gooden. Petro is actually a better defensive rebounder, and is a better defender. His size would probably be a better fit next to Randolph.
That's the one position battle heading into pre-season that this team would look to work out. The good thing is, Sacramento has five quality NBA big men -- all of whom are top-level rebounders -- plus Rashard Lewis.
EDIT: Also, people use words like "liability" too freely, I think. To me, "liability" suggests that a player is a turnstyle on defense. Mike Bibby is a liability. Jose Calderon is a liability. Carlos Boozer is a guy who doesn't shut anybody down, but who makes opponents work hard and who holds guys to about their scoring average (and who dominates almost all opponents on the boards).