My 50" print was from a 10MP file (Canon 5D classic, ISO800), that makes it about 80ppi. It looks awesome, even up close. It's a full length shot of two people, taking up 1/4 the frame, landscape shot, I can almost count the hairs on their head. It was well lit though, off camera lighting in front of a sunset.
Asus eee pad transformer iPod 2G Windows 7 PC Lots and lots of Nikon camera gear