I don't use Dropbox here's why.
1) I don't have to signup
2) I don't need to install bloatware.
3) If I install the bloatware I don't want all my "My Documents" files automatically uploaded which can easily happen if you aren't careful in installing.
4) I don't any third party upload app have access to my files.
5) I don't want dropbox client slowing down my PC (just like Gobbler doing this either so I don't use it)
6) Dropbox is very good at pushing their client at non dropbox customers, forcing some people to have to install the client, in some instances people just won't install dropbox for the file (I am one of them). Yes I know you can supply links nowadays..
7) With wetransfer I just need to point to a file, and type in my email address twice. That is all.
8) Wetransfer will automatically delete my file after a few weeks.
9) Wetransfer is simple and non confusing, even for the non technical.
Well there you go, clearly an advert for weTransfer.