I was actually surprised to see myself among the minority with large Steam libraries in the poll.
The count is at 130, but about 25+ of those are filler(expansions and source-engine copies - plenty of 'not-great-games' or collection-type filler in the 100+ remaining), still 100+ anyways. I got Steam in May, when it came out for Mac so... you might say I have issues. Every game I own with it was on sale or free, and my collection includes things like the Valve complete pack, The THQ collection, and a bunch of indie packs from the Christmas sale. The biggest draw has got to be SteamPlay, which means that if I want better operability with the Windows version, I can always have it in the future. Occasionally it means I can play with Windows users online, provided the patch is up-to-date (see Civ 5).
I don't really love Steam, I was somewhat surprised by the little issues it has - like the stoppage of downloads previously mentioned (and the work around which I give many thanks for). Although they really got me started on Mac games again, I also feel they're coming up short in that department. Some of it is issues with the porting teams who refuse to publish on Steam, so it's not all of Valve's fault. Though I wish they had at least completed coding for all of the Valve developed games (no Mac Half-Life: Source, for example).
Being a mac user, it's associative features like auto-update aren't a big deal. I also have few friends on Steam (to merit things like cross-chat and user profiles), but hopefully that will change in the future. It's library (which is really absolutely necessary for this type of application) is okay, but it has some bug issues and I wish I was able to put games in multiple categories. One of the worst things about Steam's usability are the access to feedback (outside of forums) and bug reports. Too many clicks and hidden menus for the average user.
The nature of Steam itself is one thing that will prevent me from ever swearing by it. Of course, the DRM enabling nature of it is probably the same reason it can afford all of it's sales. But again, the games themselves will suffer due to the need to run a background application at all times. Most disturbingly though, is that any release can contain additional DRM in the form of Securom, Windows Live, or any number of other parasitic 'protection'. Doesn't prevent me from buying them necessarily though. I run Wine, which provides it's own environment to anything you install within it, so while it's taking up space, at least it's not running all the time. I'll probably run a virtual system when I get Windows. I should Steam is required for some retail games. This should be absolutely optional and really the greatest detractor to the service.
I don't really wish for it to be a monopolistic force like Microsoft (Windows), so I try to shop around... if the discount isn't too enticing anyways. GamersGate, Impulse, and Good Old Games, all provide certain titles without DRM, and I'll especially back GOG when it comes to that. Collectively, they too have sales, though generally prices aren't as sexy (or fair mind you), but it's something I think all gamers should watch for. That's not to say Steam's prices are always best, the new games in particular can be quite atrociously expensive.
Another poster had mentioned that games which you already own don't automatically sync with Steam. Well, to my surprise, Braid, which I had previously downloaded a demo for through other sources, had all of it's progress intact (without manually moving save-files), so the capability is there. There are also certain publishers who assign game keys... does this mean you can download and register the games without Steam? Does anyone have an example?
When Steam comes to PS3, it may be the biggest turning point seen in gaming in awhile, so we'll all have to stay tuned.
