From what I could gather there, it seems that, while they're signing up people, they need more investment to keep going, and no one believes that they'll be able to raise more investment any time soon. And it might be true. Signing up 200 free accounts per week may translate in to $0/month revenue (or -$x/month if you count expenses), so 'signups per week' isn't a great metric to judge on, although it's the only one we've been given.
Mint started out as not profitable in any way, and I believe at their IPO (which was ~18 months later) they had an ARPU of something like 35-40$ per annum.
You need to reach a critical mass in users before you can take action on certain potential profit centers. It's different for every industry and every business, but there's some things that would be more trouble than they're worth at 25k users but start making you a lot of money at 100k users.
Mint is pretty solidly B2C. B2C companies generally shoot for 3 orders of magnitude (if not more) users than B2B. I agree if revenue is mainly due to leadgen (say, a mortgage market), a B2C product ends up looking more like a B2B product (once leads are qualified) in terms of ARPU and sales strategy, but Mint was in the shallow end of that pool.
Also, Mint never IPO'd; they sold to Intuit (the "old" competitor in their field, with Quicken) for about $200mm. Nice money, but it was argued by a lot of people that they could have hit $1-2b in an IPO. We'll never know.