I played around with about 300 trees generated out of a trunk, a branch and leaves. -> I had about 12000 models in my scene with all together about 200k faces...
It run with about 25fps on my system

As long as you are a bit carefull especially with the number of models, there shouldn´t be a big problem

Lite-C Tut. 1 Lite-C Tut. 2 Lite-C Tut. 3 (en)
Shader Tutorial (ger)

http://www.slindev.com