I sometimes play free demos/freeware on my iPhone and I enjoy it for a while. Fruit Ninja, Angry Birds, other simple stuff... it's really not that bad, just nothing you'd play forever. If these games were released on, for instance, the Super Nintendo in 1993, they would've become classics and people would worship them - that's my opinion.
However, I have one rule: Never pay for downloads. I never buy programs, games, music or movies on iTunes, Steam, XBLA, PSN, Virtual Console etc. I believe it's a brilliant marketing strategy from the distributor's perspective: Next to ZERO variable costs for distribution and 100% profit from each sale after the break-even point had been reached. I would have done the same if I was in their position.
But not only as a collector but also as a normal customer, I think it's the worst thing that has ever happened to the consumer market. People are sometimes (if the product is download-exclusive) forced to pay horrendous prices for something that costs the developer nothing at all.
For example, I hate it when people freak out over the superb "Steam Sale". Only $29 for Max Payne 3, woohoo. It's a download... it doesn't cost them any money to provide the download link - other than if they'd have to make a case, a manual, a disc and put it in the store next to you. Yet it still costs more than half of what the physical copy costs. A good deal? I don't think so. Buying a physical copy means you trade a thing for a thing. Both things are worth some amount of money, so you could sell that thing on to someone else. But a download is completely worthless once you bought it.
Imagine you could only choose between buying car X for $50,000 or renting car X for $30,000. You pay $50k to own it - but you could resell it. But if you pay the high price of $30k, you still don't even own it. You are just allowed to use it until time Y, then you lost the car AND $30,000. Nobody would ever do that because it's a bad deal. But when it's not $30,000 but $30, people care less, of course - and that's very exploitable.