My feelings on the cards seems to mirror Rich's and Josh's. You're either playing with real magic cards or fake magic cards. Real magic cards have real value. All tournaments should be played with real magic cards. For kitchen table magic or a cube, if you want to play with a fake black lotus, go for it. It doesn't matter to me if you write "Black Lotus" on an island, print one out online, find some cool new art for it, or use a fake one.
The quality of the fake cards has been improving greatly though, and I do think that is troubling in some ways. There are lots of people who do try to sneak fake cards into sanctioned tournaments. Perhaps more importantly, as the quality of the cards improves, it complicates the market for people who want to buy the real cards as they now have to be very careful. I played with some fakes last week, and while you could tell the difference side by side, the quality of the fakes was still remarkable and I'm sure they're improving.
I've been thinking of building a powered cube at some point, which means coming up with some type of proxies for the powered stuff. I'm considering going the fake route, since they're cheap and easy as hell, and I don't think there is a problem with it as long as I'm not trying to brag about having some awesome expensive powered cube and act all cool. But I would be interested in cool alternate art/proxies if anyone has a good lead on where to buy or easy ways to print them. It would be pretty cool to have full art power that are obvious proxies, but look sick. I looked on ebay and etsy and there isn't much there though.