What makes IT Services Companies Great?

IT Services companies come in many shapes and sizes. From a single person operations to giant collections of consultants and technologists.
There is also an equally large diversity in the degree of success of these companies.

Some questions that gnaw at us..

What makes an IT services company successful, and seen to be a leader?
Does being successful make it a leader?
Or is it the other way around - being seen to be a leader in a specific area ensures its success?
What role does visibility of the brand play in ensuring its success?
Do these companies, prior to being successful, even have a 'brand'? or only a company identifier?
Which are the channels these successful companies use to get their messages across?
What role, if any, advertisement play in building these brands?
Do customers really percieve these 'brands' the same way as the organizations' employees see themselves as?

Lets attempt to address these questions over a period of time.