Dropbox is great. Simple to use. Always reliable in my experience. The user experience is really smooth and intuitive. They have emerged as the market leader in many ways, and I can understand why. I do wish they would give me more free space, but I can't be greedy! Love the service.
Been using dropbox since it came out and have never had a problem. It's mobile apps work like a charm. Also the ability to recover a file that was deleted has saved me countless times at work.Recently upgraded to Dropbox for teams at my company (21 person startup) and have had no complaints from anyone.
Dropbox is absolutely fantastic. The fact that users can easily share files with each other and developers can create DropBox apps with their API and get access to essential user files is really well thought out. It's a reliable and well-designed servie.