Valve's Steam was derided by many upon release for being buggy and slow, but underneath that was a delicious digital software delivery platform that I love and adore.
Previously, hating swapping CDs all the time, I made CD or DVD images of all the software I bought, store the keys somewhere secure, dumped the physical media in the bin and used daemon-tools to mount the images in a virtual drive whenever I needed them. This was frequently fraught with difficulty, as the content-owners regarded the media as the token of ownership, so copy-protection schemes hated it, but it was just so incredibly convenient (and fast) that I just stopped buying software that didn't support this mode of use.
Digital delivery of titles was a decent promise, but services like direct2drive foul it up by limiting use to one machine at a time, which is less freedom than being able to install media-based software on your multiple computers. Steam, however, is digital software delivery done right - you download the tiny Steam client and after logging in, you see all the software you've purchased - you can then pick and choose which to install on the machine, and you're done. No accusations of piracy, quick purchase, fast downloads, and you're free from machine-dependence. It's so quick and easy that despite its (incredibly) limited library, buying software any other way just seems insulting.
If it did savegame syncronisation across your multiple machines, I'd probably die.
