For several reasons already mentioned by others, I think there is very little chance this is ever a "forgotten" championship, even if the C's fail to win another title in the KG-Pierce era (Ray is a worthy 3rd member of the Trinity, and a probably Hall of Famer, but Rondo is likely to be the 3rd most important player on any future C's title teams, even if they win in 2009). Which, for the record, I find unlikely; I'd be surprised if they didn't win at least once more over the next 3 years.
KG is top-five all time at PF, and Pierce will likely retire as the #2 career scorer for the most decorated franchise in the sport. The return of the Celts to the top of the mountain after 20+ years, and beating the Lakers to do it, will also be remembered.
Even beyond those circumstances, though, the team was just too dominant to be forgotten. The 2007-08 Celtics were one of the ten best NBA teams of all time, by practically any combined regular- and post-season measure you can come up with.
For comparison, the '71 Bucks sure as hell won't be forgotten as a great championship team by anyone who knows what they're talking about, because they're another of the ten best teams all-time, with the same 66-16 record and featuring too all-time-great players in Kareem and Oscar Robertson. But they still lack the "4th Celtic championship generation" angle that will end up being the strongest argument.
The other team that I see as a potential parallel is the '83 Sixers, another historically dominant regular season team (65-17, coupled with only one playoff loss) and provided the only NBA title for two league MVPs and Hall-of-Famers in the Dr. J and Moses Malone (Dr. J won 2 ABA titles with the Nets, of course, and lost in 3 NBA finals with Philly before Malone arrived in '82-'83)
Ultimately, though, I expect that all of this is moot, because as I already said, I fully expect the C's to win at least one more title while KG and Pierce are the star players, and that will cement their place as THE team of the late 2000's.