I have recently asked a colleague to share one of her publications with me. I did not hear from her, but after a week or so, while cleaning my @SaneLater box, I discovered an email sent by her from an unfamiliar address and in another language containing a link to the paper. The story was that the file she wanted to send was too large for her regular email provider. So she used one of the many services which allow to upload a file to a server and then email a link to this file to your contact for download. I myself used one of such services (YouSendIt) once upon a time. All in all, the procedure was pretty clumsy: you needed to set up an account with such services (sometimes even pay for it) and the emails they generated could come from strange addresses (thus ending up in @SaneLater or even in Spam) and sometimes contain ads.
All you have to do is to make sure the file (or even folder) that you want to share is in your Dropbox (I keep all my mission-critical files in the Dropbox anyway), right-click on it (or use the Dropbox icon in your Finder’s toolbar) and select Share Dropbox Link. The link to the file or folder will be copied to your clipboard and can be emailed (or Skyped, SMSed, etc.). There is no need to upload anything, not even to open a Web browser. The persons you’re sharing with do not need to have a Dropbox account: they will be able to access and download the files directly through their web browser! And if they do have a Dropbox account they will have an option to simply add the shared folder to their own Dropbox and thus have it all on their local drive without the bother of download.