David Carr signing this week was a positive step for Carolina. They finally filled a need in free agency, they finally landed a player they pursued, and they have legitimately made progress toward upgrading. All of these things have been sorely missed this quiet offseason, an offseason that's gotten much more busy in the past week.
Key to that business is speculation(Sportscenter stated QB controversy, NFL Total Access blazed "Carr v/s Delhomme" as a headline, nfl.com stated Carolina having the "best QB tandem in the league"), and it won't get any smarter or more reasonable from here. The end result is that this is still Delhomme's team - he has to play better, but that's not about Carr's presence. Delhomme has to stumble significantly to lose his job.
If Delhomme falters and Carr steps up, it's still a positive for the team. A younger QB with a year's more experience on the field, Carr's emergence would mean fixing his problems - slow getting the ball out of his hands, taking too many sacks, locking onto receivers, and relative inability to make reads/analyze a defense.
Nonetheless, dumping Delhomme's contract simply means paying Carr that level or more - the market has gone up considerably since 2004's signing (just ask Steve Smith). And with many similarities to Delhomme but without the playmaking, Carr's sudden revival doesn't seem as likely as some may expect. And with a two year deal, he's signed shorter term than Delhomme; the ideal of Delhomme being succeeded by Carr in a natural progression is highly unlikely. There's no reason to believe Delhomme will not physically be able in two years.