I will pay for the service, but only after I've exhausted my X free gigabytes. I'm extending that as far as I can by referring people, and thus getting 250MB more free space for each referral.
If you haven't signed up yet, use my referral link, and you'll get 250MB extra free too :-)
Someone voted me down, but it's a serious question.
An inherent part of the "freemium" model is the "free" bit. The point is to entice people in further. It's up to you the service offerer to make the pay service so compelling that people want to switch to it. It's completely wrongheaded to look at the people who aren't willing to pay and say they are the problem, or say or imply that they are leaching or ungrateful.
You are enticing people in, if you don't have what it takes to then transform them into paying customers, and you don't want to pay for their ongoing use, then perhaps you should switch to a free-trial instead of a free service.
I'd pay for it if they had a plan in between 2GB and 50GB. I want more like 10GB for like $2/month or something - the big plan is too big, so I'd rather not give them $8 extra per month out of the goodness of my heart.
That said, I wouldn't pay for this service.