It's a very vocal group of people; how large it is is hard to say, but they'll be complaining heavily about it, pretty much guaranteed.

The very idea that a website might want to take good ideas from elsewhere, make itself user friendly and attract more users in order to remain a going concern is simply anathema to some of the userbase, who look back to the halcyon days when LJ was perfect and forget how little competition there was, etc.

'Fey is right, there are some who will complain it's making it like MySpace, facebook, an intrusion into privacy, are averse to any sort of rating system, etc etc.

I predict a petition/anti comm almost immediately after it's announced.