In an eight team playoff (heck, even a sixteen team playoff), the regular season would be FAR from meaningless.
Going with the sixteen-team tournament example, there are eleven FBS conferences; we'll take their champions and five at larges. No meaning is taken out of the conference schedule, as for the current BCS conferences there are automatically BCS bowl tie-ins. The regular season for non-BCS schools in FBS would actually become MORE meaningful because the winner of the conference would have a fair chance at the national title.
At this point, there'd be five at-large teams who could be selected using the existing BCS formula; we'd just take the top five remaining teams that weren't conference champions. The teams would finally be seeded according to the BCS standings.
Following this example, the playoffs teams from last season (using the 7 December 2008 BCS numbers) would have been as follows:
1 - Oklahoma (Big XII Champs)
16 - Troy (Sun Belt Champs)
8 - Penn State (Big Ten Champs)
9 - Boise State (WAC Champs)
5 - USC (Pac10 Champs)
12 - Cincinnati (Big East Champs)
4 - Texas (At-Large)
13 - Virginia Tech (ACC Champs)
3 - Alabama (At-Large)
14 - East Carolina (C-USA Champs)
6 - Utah (Mountain West Champs)
11 - TCU (At-Large)
7 - Texas Tech (At-Large)
10 - Ohio State (At-Large)
2 - Florida (SEC Champs)
15 - Buffalo (MAC Champs)
Don't tell me that this tournament wouldn't make money, because you'd be wrong. It wouldn't take any longer than running the NFL Playoffs, either; you could run the games in weekends and have the other lesser bowl games take place during the week leading up to the playoff games on Saturday. This tournament also doesn't make the regular season useless; you either have to either win your conference or be one of the very best teams that didn't in order to qualify. Finally, this playoff would naturally reduce the number of bowls since more teams would be in play to win the national title and thus not available for traditional (meaningless?) bowl postseason play.
I realize that if any playoff comes about, it will probably be eight teams, but I'm using the sixteen team tournament to make a point that this can work. People would watch it, and it would make money.