One example for me is digg.com.

On one hand I find many of the articles interesting to read, but on the other hand I think the demographic of digg users (and their comments) feel too homogeneous. For example there is a heavy male gender slant for starters, and also a heavy liberal and non-religious slant as well.

I happen to be male, liberal, and non-religious, but I wish there were other types of people on there to balance it out.

Well, now that I think about it, I need to do a little balancing on MajorIndulgence because I can't be the only one posting! Need marketing ideas!