Without jailbreaking my wife's iPad, can't load a Playstation emulator on it. She saw me playing Chrono Trigger on my Playbook, and said she wanted that for her iPad.
Couldn't find a way to do it without jailbreaking it, which she won't allow.
Most Emulators are legal, they are just a program which emulates hardware. So if its not using or distributing with any leaked code or System files of the original console its not illegal.
Well roms on the other side are in most cases illegal, but this also depends on the country your living in. If you own the original game its legal in many countries to create a backup of it and play it with whatever you want.
But yeah most roms are downloaded by people who dont own the original game