Let's go down the list, shall we?
Bungie: Arguably their best purchase. The only problem is that if they are not making Halo, they aren't making anything.
Rare: This should be their best asset, but for some reason they decided that the platform to on which to put their best stuff is the GBA. On the Xbox horizon? One mediocre game released, another game on the way, and a remake of a game that was released but 3 years ago.
Curlymonsters: Unfamiliar? They made this game called Quantum Redshift, which I will admit it is a very decent F-Zero clone, even down to the "comic book" presentation which F-Zero had in 1991. They were working on Quantum Redshift 2, which had all this neat stuff in it, but Microsoft didn't like it, so they pulled the plug. On Curlymonsters. Now imagine if they had that kind of power over a certain other game company, hm?
OddWorld Inhabitants: Well these guys dropped of the face of the Earth, didn't they? I seem to remember after their launch debut of Munch's Odyssee, their next game was a GBA game. And I think there was some talk about the PS2... But I can't be arsed to remember. Anyway, it's all pretty much speculation and rumor as to what they and their illustrious leader Lorne Lanning have been up to, because they all but disappeared.
There are more companies MS owns, I think, but none of them have done anything worthwhile, I dunno, maybe those PGR2 guys (neat) and those guys that made Azurik and Nightcaster (blech). But really, it doesn't look good for companies owned by MS, even if they get wads of cash, the turnout isn't exactly great.