I would like to think that the success of the Humble Indie Bundle, among other things, prove that DRM is unnecessary. That might be being a bit of a logical stretch, however. There are many reasons for people to contribute to the Humble Indie Bundle including simply to support the sales strategy, and because it was highly publicised on the internet. As such, this result doesn't really prove anything about an environment where such behaviour is the norm.
Despite this, I firmly believe that DRM is not only unnecessary, but actively harmful. Firstly, I think in many cases allowing the noncommercial copying of a work increases awareness of it, and as such encourages continued sales, and a community. DRM interferes with this natural spread of a work's popularity, and paying game reviewers to rave about a game is unlikely to work as an effective substitute. People trust their friends' taste in games more than IGN, usually. Secondly, DRM is (generally) ineffective in preventing piracy of a work, instead only inconveniencing and/or alienating your existing customer base. Even in situations where the DRM prevents pirates from playing for an extended period of time (such as Assassin's Creed II), it usually has a much more harmful impact on existing customers (again, see Assassin's Creed II). This makes them more likely to resort to piracy for future works, and leads to a bad relationship with the company.
While Steam is generally touted as an example of DRM done right (that is, relatively unintrusive, and providing additional value) I would argue that all the services provided by Steam could equally well be provided by a platform unencumbered by DRM. GOG.com (as mentioned in my previous post) sells older, classic games fully DRM free. It ties purchases to your user account, allowing you to redownload any games you've previously purchased as long as their servers are up (the same restriction applies to Steam -- if their servers go down, the service of being able to redownload games you've bought but deleted will be unavailable). This is one of the features of Steam that is commonly cited as making up for the DRM they apply to the content they make available. The other aspects -- the user community and rich selection of indie titles -- could equally be provided without DRM.
From your comment, it sounds as if you think I am under the misimpression that DRM is an unfortunate necessity in the marketplace. This is incorrect -- I believe it is possible, and in fact easier, to have a vibrant content industry without the use of such restrictive, anti-social measures as Digital Restrictions Management. If you merely hit reply, and that's why your post looks like a response to mine, then I apologise
As you were!
PS: I apologise for the length of this post. I do not have the time to reword it more concisely. Exam in ten minutes <_<