Sub Domains - Pros? Cons?

What are all the pros and cons of building sub domains?

[RobbieD]

Just wondering what the pros and cons were of building sub domians off your main domain if you have REAL CONTENT on the sub domains?

Do the directories like it? Do the search engines like it?

I know for one it is easier for your users to remember...

chat.domain.com

[Reflect]

My thoughts on this were:

*Makes it easier for the user
*Makes the sub domain and the TLD tighter on the "theme" aspect
*Makes link exchanges easier as then sub is more focused.

All of the above is only IMHO,

Brian