I just purchased my first digital HDTV and am VERY happy with the picture quality using an antenna to receive over-the-air broadcasts. I read one review of the TV I purchased that mentioned it changes channels rapidly. My question is what speed is considered "rapid" versus "average" when changing from one digital channel to another? [I set my TV's tuner to only receive the digital channels.] My TV sometimes requires a couple of seconds and sometimes is much faster. Thanks.

Digital TV tuners are slower than older cable or analog TV tuners. Due to local station PSIP issues, it can sometimes take longer than others.

The ch changing speed is also sometimes influenced by signal strength - higher signal strength -> faster ch change. 1-2 sec is probably avg.

Also digital signals are compressed and consist of both full frames of data and partial frame updates so in addition to other issues there is delay based on when the first full frame of data is received.
It also takes some clock time to peforrm the decompresion of the video and more clock time if the resolution of the program being received is different from the native resolutioin of the TV to scale to the other resolution.

Channel changing speed all depends on your tuner. Some are fast, some are slow.