I've always believed that consistency matters, whether it be at the architecture or the technology level. Its just much easier to manage a team with differing abilities if there is a consistent model and implementation.
I'm fortunate however in that I've picked technologies that actually work. Pity two fools that I heard on the floor of JavaOne (Moscone South if I remember correctly) they were arguing, well lets say talking at each other, about the merits of two different Ajax libraries (I have no clue which). The discussion was annoyingly loud and annoyingly stupid. At one stage however there was a work of genius
One chap (lets call him Fred) said
"Yeah, but at least we agree that you can do anything in Ajax"
To which his friend (lets call him Bert) said
"Yeah, there isn't anything you can't do"
A chap wandering past threw in one of those conversation grenades that leave the discussion dead and the participants suffering shell shock
"Try writing a VOIP client"
Personally I nearly exploded trying to hold in the belly laugh that wanted to get out. The point was brilliantly made. Consistency is good, but make sure you are at least in the right technology ball-park for the problem you are trying to solve.
Consistency matters, but don't be consistently stupid