Blog is not enough. What Mint did (and is still doing) is selling their byproduct - in their case is statistics they can dig from their user data.
Statistics are always very popular among the press crowd - this can be easily sold and drives additional traffic.
Re:How Mint.com Acquired 1.5M+ Users
by angelhaze218 on Thursday March 25, 2010 @11:28PM
(#1220178)
the nature of blogs is that they are essentially miniature social media networks in disguise, when done right. Facebook is a giant "blog", that's why they don't need any blogs.
That said I know they have blogs now, largely targeted at developers and early adopters, but in the early days they didn't. However, I'm a big fan of blogs, think every professional/company should have one. Great way to spread ideas, make contacts, etc.