finally, I was about to drop dropbox because I am running out of space.
I absolutely love the service, but their prices are just 2-3 times above the competition. I would buy the 100 GB in a heartbeat if it would be 50-70 USD a year.
It means that there must be a 10:1 ish ratio of free to paid accounts which probably prevents them from dropping the price.
Arguably though, the service would be less valuable if everyone had to have a paid account before you could share files with them.