Fun fact: email is not a file transfer protocol. When you use it to send files around, weird (and sometimes bad) stuff happens. Attachments can contain viruses. They take a lot of bandwidth to send (especially if you're CCing them to a lot of people), and that means that everything is slow, and that makes admins suspicious. (Sure, they're a suspicious lot by nature, but they make the Internet go, so we try not to make them mad as a rule.)
But, for a lot of people, attaching a file to an email is the only way they know to send a file to someone else. How else can you get a file to someone besides email?
The very best way to transfer a file is to open a connection directly from the computer that has it, to the computer that wants it. That way, only the two computers that need to handle it do, by talking directly to each other. (When you email a file, three, four or maybe more different computers will handle that message.)
If you're talking to someone on IM, you may not realize it, but you're already using one of the easiest file transfer mechanisms around! Just drop the file you want to share into your chat, and you'll immediately prompt them to start downloading the file from you. It works for pictures, music, Word documents, even short movies. Drag-and-drop!
But, what if you aren't both online at the same time? Well, there are still plenty of options out there.
As digital cameras become more and more sophisticated, even emailing pictures can generate huge messages. Using one of the photo sharing services or social networking sites, like Flickr, Picasa, Kodak Gallery, Snapfish or Facebook, means you get access to their handy tools (like ordering prints!) It also means that the people who you're sharing photos with have an easy place to see all your pictures over time (so that adorable picture from last Thanksgiving can be looked at again when you email them a link to this year's pumpkin pictures.) With an extensive range of privacy options, it's also really easy to make sure people have to log in with a password to see your pictures.
Just want to share some regular old files? Apple's iDisk or Joyent's BingoDisk let you share files publicly or privately (and provide an off-site backup, should your computer fail.) A third option, Dropbox, even provides 2GB of free storage to anyone who sets up an account -- plenty for any basic file-sharing you may need to do.
There are other benefits to sharing this way, too. It's easier to make changes, and know that someone is looking at or downloading your most up-to-date version. Some sites will provide you with statistics, so you can see how often a file is being looked at.
Know other easy, non-email ways to share files? Leave a comment!