I like to stay out of the legality debate, but here's my two cents:
I don't see a problem with it being hosted. We already host covers for the M3 Simply and R4 for the DS, which are homebrew launchers just like this is. While you can load it on with every game and thus not have to ever buy the originals, I don't condone that nor do I really think its a great idea.
The powerpak isn't all incompassing as one would hope. It currently will run around 80% of the NES library (though that does include the US library and European PAL liberary and Japanese Famicom library) but there are still quite a few games that don't work with it.
Why is the powerpak worth checking out if not for those reasons? The NES is over twenty years old now. Old games that are dirty and difficult to get to work can be played easily with a powerpak. Ever had your Final Fantasy save data dissipear because you didn't hold in reset while turing it off? That's no longer important, as the powerpak saves the save files to flash memory, which can even be stored on your computer as backup. The Powerpak has Gamegenie built right in for support up to five codes, two more than the real version.
The biggest reason in my opinion to use the powerpak is to save ware and tear on your old precious games. My NES collection is 200+ as is my Famicom collection. Even though the powerpak can play almost all of them by itself, I still keep them around because much like the Vertual console or Xbox live arcade, not owning the physical copy of a game is somehow unsettling for me.
