At least www.vimm.net has it, and it works, and that site has no porn banners. 
And yes, I've played it. Surprisingly good conversion actually. Sure the graphics are quite crappy when compared to the original, and the interface isn't the greatest, but considering how few adventure games NES has, it's a nice addition.
As for Maniac Mansion, I have it's Swedish version on the original cartridge. It started my interest in adventure games, by the way. ^^

And yes, I've played it. Surprisingly good conversion actually. Sure the graphics are quite crappy when compared to the original, and the interface isn't the greatest, but considering how few adventure games NES has, it's a nice addition.
As for Maniac Mansion, I have it's Swedish version on the original cartridge. It started my interest in adventure games, by the way. ^^