I like K-Mart as a player - I do really like the toughness and attitude he brings to the game, and as with the above comments I do think a Rondo/Bradley/Pierce/K-Mart/KG starting lineup would be an absolute nightmare for other teams to play against.
Looking at his advanced stats he's a slightly better rebounder and shot blocker then Bass, while he's a much more capable scorer in the paint - something we really could use.
Martin also also gives us a pure defensive presence at the PF forward position, and that's something we don't really have right now. We have Bass, Sulinger, Wilcox and Green as our primary PF candidates, and neither of those guys is really known for their interior defense.
The only problem I see with the signing is depth - or more specifically, too much of it. Even if we use Wilcox as our promimary back up at C and Martin as a primary backup PF, that pretty much eliminates Sulinger's hope of getting playing time. It also limits Green's potential playing time to ~20 MPG as a backup to Peirce, as you can be sure Doc initially wanted him to spend some time at PF.
Still, in recent times Doc and Ainge have always been of the mindset 'you can never have too much talent', so I would not be surprised at all if they pick up Martin given the opportunity. It would give us the flexibility to have two big men injured and STILL have one of the deepesst frontcourts in the NBA.
Initially the depth issue concerned me (too many players at PF) but the more I think about this deal the more I like it - I really think KMart (along with Collins) would help to give Boston some of that 'enforcer' mentality that they lost with Perkins, and that's something I'd love to see!
It's hard to imagine Kmart signing in LA where he'd clearly be a third string PF behind Gasol and Jamison. In Boston he'd likely back up Bass as the first PF off the bench, and should get a consistent ~10 MPG or more.
I'm more concerned about him hitching a ride to Miami where he could potentially start at PF (alongside Bosh) and give Miami some much needed toughness and inside presence...that's exactly what they need to take them to another level, and I would hate to see him go there!!