Most HD cable, satellite, and over the air signals are broadcast in 720P (1080i) not 1080P. The most common source for 1080P is the Blu-ray DVD format. So, on broadcast HD, you won't see much difference between a 720P or 1080P projector.
Difference between 720p and 1080p projectors?
I've had an Optoma H79 projector for 5 years and it still works great, but I'm wondering how much video quality difference is there between it's 720p resolution and newer projectors offering 1080p. And is there a very noticable visual difference/improvement or essentially the same?