how many plecos is too many?

[Noddy]

Plecos are territorial and don't live in congregations in the wild.

i guess most of them don't, but these guys do not share your opinion, i think!
http://www.youtube.com/watch?v=HqgjgN7HIig

But in a tank is a dif situation. They'll fight hard over territory.
I keep an Hypostomus and a Pseudacanthicus in a 6' tank and it's barely enough.
Gibbi's and commons will need an even larger tank.