Carr was running the first team offense on the first day of Houston's mini camp. He's already their starter.
I'll add to this. Starting QBs I would take over Jay Fiedler:
AFC East:
1. Drew Bledsoe
2. Tom Brady
AFC Central:
1. Tim Couch
2. Jeff Blake
AFC West:
1. Rich Gannon (though I'm not real crazy about him)
2. Trent Green
3. Drew Brees
4. Brian Griese
AFC South:
1. Peyton Manning
2. Steve McNair
3. Mark Brunell
4. David Carr (much more potential than Fiedler)
NFC East:
1. Donovan McNabb
2. Kerry Collins
3. Patrick Ramsey (potential again)
NFC Central:
1. Brett Farve
2. Daunte Culpepper
3. Joey Harrington (potential again)
4. Chris Chandler
NFC West:
1. Kurt Warner
2. Jeff Garcia
3. Jake Plummer (and I'm not real crazy about him either)
NFC South:
1. Aaron Brooks
2. Michael Vick
3. Brad Johnson
So, that's 25 starting QBs (I really should leave out Ramsey, but I'd start him over Fiedler) that I would take over Fiedler. IMO, Fiedler is at the same level as guys such as Matt Hasselbeck, John Kitna, Kordell Stewart (last year = FLUKE), Chris Weinke, Vinny Testaverde, and Quincy Carter.