I noticed some issues with streaming ... from my MacBook Air ... the iPad streaming works fine.
when streaming from the air using mirroring, it's going to be jerky and missing frames, mirroring basically sets up a virtual camera inside the video card and records the screen image, then converts and streams it in real time, it sacrifices quality (and frames) to maintain sync between your computer monitor and the remote TV screen. and also because it's a quick encode, it's also not as optimized as it can be, so it will be a larger file.
when airplaying from your ipad, it takes a pre-encoded stream and forwards that file directly to the aTV (or tells the aTV where to find the stream on the web, and then the aTV will download it directly)
if you're watching a digital stream on the web, even if it's "live" they'll take an extra bit of time to process a good stream, maybe only a 1/2 second, but it's enough to get a better quality. but that would be enough to annoy the crap out of you if you were watching 2 screens beside each other like you do with airplay.
If you were to compare a digital cable box, analog cable into the tv, a live web-stream and an antenna pulling the signal off the air of the exact same broadcast, you would find vastly different timing in when it hits the screen.