I'm ambivalent about buying a hardcopy disk vs. just buying/downloading from Steam- I'm kinda oldschool, been buying disks forever... but I'm starting to think there's not a whole lot of point to it, anymore. I do like Steam. I guess if I'm buying a new game that's just come out, I'd go with the DVD in a box. But if the game's been out for a while, and it's already started to appear in Steam sales... then for sure I'm gonna buy a game for 33% off... or 50%... or even 75%, sometimes. I've never seen bargains like that in brick 'n mortar game stores, personally. They don't have any of those in this small-ish town, anyway. And I wouldn't spend $10 for gas to drive to another bigger town to maybe save $5 on a boxed game, that's for sure.
If you have good broadband bandwidth, it's not really worth it to bother with boxed disks, in my opinion. Will Valve croak in the near future? Pffft. They're healthier than Microsoft, in terms of increased product sales/customer growth percentages, via Steam. They've been around since the mid 1990's, and have only been getting steadily stronger, exponentially. The only other game company doing better than them (maybe? not sure anymore) is Blizzard. Those two are the titans of modern PC gaming. So I'm not particularly worried about it.