While DropBox's basic setup gives you 2GB to start with, they make it very easy to bump that up to as much as 18GB as a free user. Their pricing, beyond this free service, is very competitive. Enterprise teams with needs for large storage (100GB - 1 TB) have multiple pricing options. I have never experienced downtime (though there have been issues - see CONS), and have been using the service happily for over 2 years. The DropBox community has also created many addon services that can be used to add functionality (send to dropbox allows you to email files to your account).
Room for Improvement:
There have been a few privacy and security issues that have soured me a bit on dropbox over the last year or so. First, there was the admission that dropbox was analyzing each file uploaded to see if there was already a version on their servers. If there was, they were linking my file to the original file, rather than storing multiple versions of files across users. Later, there was an error in a code update that allowed all dropbox accounts to be accessed without passwords for a number of hours.There have been many criticisms over the type of encryption that DropBox uses as well. If you are backing up your companies data to a cloud storage solution you have to be sure that you agree with their policies for encryption. DropBox might not meet your criteria.
With Google giving every user 5GB to start in their Drive accounts, DropBox certainly has many companies targeting their business model. Anytime you store your data in a place that you don't own, you lose a certain amount of control. Any business looking to use DropBox as its only form of data storage or backup, must consider what type of data it must control on its own.
Disclosure: I am a real user, and this review is based on my own experience and opinions.
Jul 17 2012