Good deal. I have done this twice. My friends and I strategically plan to start and end at the same meal (2 dinners or 2 lunches).
This promotion pays for itself if you can hit at least 3 buffets.
It's a great promotion for Harrah's because they know many people will feel the need to gamble as you walk through the entire casino just to arrive at the buffet in the rear of the casino (except Rio where the Strip shuttle drops off at Carnival World Buffet).
Good:
#1 - Caesar Palace's Lago lunch
#2 - Paris Buffet dinner
Pass:
Rio Carnival World Buffet
Harrah's Flavor Buffet
Flamingo Paradise Buffet
Fail:
Paris Buffet lunch
Planet Hollywood Spice Market Buffet
Still hoping to try:
Caesar Palace's Lago dinner
*I have also individually reviewed each buffet. Strongly recommending trying this once while in Vegas. Only downfall, there should be an express line to allow those already paid to bypass the cash register line and queue immediately to be seated.