Being afraid to generate revenue before hitting critical mass sets this silly precedent that you can't flip the switch until you reach a mythical number of users.
I'm not saying Twitter couldn't make a bunch of money, but for every YouTube and Twitter waiting to hit it big, there are 1000's of companies thinking this is a viable solution to their problems and failing because of it.
I'm not sure I buy that. There are plenty of companies, like your own, that understand what their business needs. And there are always going to be plenty of other companies that behave like sheep. If it wasn't Twitter, they'd find some other trend to misapply.
The other thing I wonder about is if their monetization strategy involves some technical challenge. Remember, their product is relatively straightforward from a technical standpoint, not to trivialize what they've done at all, just to make the point that they have gotten here in a short period of time with a very small number of guys. What if their preferred method of monetization involves solving some technical problem that they just haven't resolved yet?