a) a target size or
b) continuous growth of some rate.
Also, should it be relative to what else is out there?
For example, should Microsoft continue its pursuit of Yahoo! (at the costs of its stock value)? Once upon a time MS was probably happy with their size, but since Google is a bigger kid on the block now, they feel they need to grow more simply to be #1 again.
Someone else recently asked why YC startups don't strive for even grander visions of Facebook proportions (the fact that is easier said than done is a different issue).
So my question is, should you as a company decide a target size/market-share to reach at which point you will be happy, or is it a continuous growth that matters more regardless of your current size (or lack thereof). And does the existence of a bigger competitor mean you must do whatever it takes to outmatch them?
Somewhat related, is the question poised by Michael Arrington as to whether YC News wanted to grow or stay under the radar.