The main reason that I buy a lot of digital games is because of the PS3's game sharing feature. I have a real life friend that I share with. We have each others accounts. Sometimes I buy the game. Sometimes he does. Sometimes we put in half.
It's better that way when buying games with co-op or games we both wanna play but don't wanna wait on the other to finish it 1st. With that said I still do buy more disc games then digital but only ones that I definitely want in my collection or ones that are disc only.
One of the major benefits of buying digital is that when you blu-ray drive goes out you can still play a lot of games without the need to repair. Also they take up less space physically of course. The downside is absolutely no resell value or even value at all besides the link to your account. But if you are nearing the time when you have to buy a 3rd PS3 this gen thanks to faulty construction than you will have ended up losing a lot of money thanks to the limitation on how many times you can download the games. That is the most negative aspect of digital distribution, the limitations on downloads and what you can do with it, that's what makes it more of a rental/subscription since you don't own the product outright forever.