One of the great things about Dropbox is that its popularity means that developers are developing other services, like DROPitTOme that are fully integrated with Dropbox. But is it an application that you should use?
Clients can upload files directly to your Dropbox
The service is similar to AirDropper. It creates a separate folder within Dropbox, but only allows the service to access that folder, not your entire Dropbox.
Once you have allowed the service access, it then creates an upload address specific to your Dropbox. Thankfully, the address also is password protected, so only individuals that you provide the password to can upload files.
As of right now, the maximum file upload size is 75 mb. Unless your client wants to upload video or a thousand-page high quality PDF, that is unlikely to pose a problem.
The program is currently in beta phase. The good news is that means it is free. The bad news is that it might have kinks that are still being worked out.
A bigger concern is a lack of discussion regarding file security. AirDropper has a fairly detailed explanation on their site about how files are treated. With DROPitTOme, I would assume that files pass through their site and into your Dropbox. As we all know, however, assumptions are never a good thing, especially when it comes to file security.
If you decide to try it out, be sure to keep those concerns in mind.