DarthFed, I agree that the weak competition argument shouldn't lessen Roger's overall greatness, but I think it is something that should be considered. I mean, look at Roger's undisputed reign - 2004-07. Who were the best players during those years? Here's a list of every player who finished in the top 5 during 2004-07 with their rankings during those four years:
Federer 1, 1, 1, 1,
Nadal 51, 2, 2, 2
Roddick 2, 3, 6, 6
Hewitt 3, 4, 20, 21
Safin 4, 12, 26, 56
Moya 5, 31, 43, 17
Davydenko 28, 5, 3, 4
Blake 97, 23, 4, 13
Ljubicic 22, 9, 5, 18
Ferrer 49, 14, 14, 5
Nalbandian 9, 6, 8, 9
(I included Nalbandian so as not to offend Cali)
So it is clear from looking at that list that Nadal was really the only other truly dominant player during Roger's four year reign, and then when Rafa fully matured and diversified his game in 2008, they were basically coeval for two years (2008-09) before Rafa jumped ahead for good in 2010.
Another way to look at it is that during most of Federer's peak years, 2004-07, there was really only one other truly elite player, and that player hadn't quite reached his prime. When he did, and when two other truly elite players came of age, then Roger was just one of four great players but not head and shoulders above the rest anymore. Of course Roger was 5-6 years older than the other three, so we'll never know how he would have fared against them if they were the same age. 2009-10 are the closest we came to all four being in their prime years, with Roger being 27-29, Rafa 22-24, Novak and Andy 21-23.