Philosopher's Stone is too tempting in a way. If you used it to make gold from lead, you would most certainly not be able to live in a first world country with any sort of an income tax; otherwise, you would be investigated for money simply appearing from no where. And you couldn't use it to live forever, because again, eventually the game is up. And once people know about it, well, all the money in the world isn't going to last you very long to afford the kind of protection you'd need from someone trying to kill you or steal the Stone. Hell, even the gold market is going to be against you, because you stand to devalue the price of gold by creating it from nothing, so soon it'd be made illegal to buy from you, and you'd have to go to extra lengths to sell it. Same if you did another high value metal like silver. I think you'd have to run a salvage/scrap company, and boost your recovery with extra scrap coming in. And at small values so as to not arise suspicion. Copper would be good, though - price on that is currently very good.
Furthermore, you could not fall in love or have children unless you planned to likewise give them the Elixir of Life. And your current family members; would you be able to let your parents die when you could keep them alive? And immortal life does not guarantee good health or even a good life. I think Flamel was healthy because he was a wizard (although granted, it never specifically states Flamel is a wizard, but I would assume so). But the more people you give the elixir to, the more people have to know your secret, the bigger chance you'd be betrayed or used. That's unfortunate to think of family, but greed can be a terrible thing. The Philosopher's Stone would only be useful if you could control yourself to use it to create small amounts of gold when you most needed it; and I don't know if it'd be worth the cost at that point.
There would be ways to hide your source of income. I don't want to delve too far into this ('cause it's late and I'm already fuzzy headed with the flu), but I don't think it would be impossible to cover up an large initial creation of gold - getting lucky gambling, for a start, would be plausible, though probably less realistic than a magical way to turn lead into gold. Besides, if you could have one item from the HP world, surely you would also have access to Gringotts and such - which would both be a way to turn gold into usable currency and a way to hide it from income taxes. I imagine there's also a way to stop wizards being investigated - cover jobs to hide their real occupations - so that sort of cover could be employed.
As for loved ones - a whole family living forever would be obvious, but picking just one other person to drink it with you seems manageable. Changing your identity completely, whilst possibly shady, is doable. And, like Flamel, I imagine living forever would eventually start to lose its appeal - that's when I'd start to give it up and settle down for another normal life. With lots of money. Probably monkey butlers. Actually, since this is the future, I would have something superior to monkey butlers. Robot butlers of some form, perhaps.
