My wife and I have noticed what seems like the occasional dropped frame or poorly interlaced frame when watching HDTV (Cablevision, HDMI connections all around). We're not entirely sure what the problem is or even how to best describe it, but from what I've read I don't think that this is judder. Rather, it seems like a 'hiccup' in the image.

We have only seen this happen when one scene cuts to another, so my wife (who works in television) suspects that it's somehow lingering on an interlaced frame and we're basically seeing both halves of the interlace at the same time, and they are interlaces from different frames.

I've been searching the forums and the internet for the last hour and have seen some discussions of some similar things, in particular with regards to ABC perhaps compressing shows to squeeze an extra commercial into an hour show.

Can anyone shed some more light on what it is that we're experiencing?

Since you did not give any details about your configuration your post is somewhat like the one on an automobile website that says my car is not getting good gas milege what is wrong.
The only thing I can say is that all digital transmissions in their record headers indicate when a scene change has occured.

We have an SA8300HD via Cablevision in Westchester County, NY.

The box is attached via HDMI to a sony HT-CT100, and that is going (also via HDMI) to a Sony KDL-46W4100.

There have not been any issues with BD or DVD (both being played off a Sony BDP-S350, HDMI through the HT-CT100 as well).

I'm not sure what you mean by a header.

Every block od data contrained in MPEGcompressed/encoded format contains data in the fromn or header of the data block about the data contained in the block. One of the pices of information is lets the decoding software know if ths is the first block from a new scene.
Do you have the problem if you bypass the receiver?
Does the problem with both 1080i and 720p HD programs or unique to a particular channel.

A good test would be to try component video instead of HDMI.

ABC does blend 2 frames into 1 at seemingly random intervals throughout almost every show in primetime. I've never seen it on any other channel, so it's probably not the same problem you're seeing. What you describe sounds like the show was edited in the 30i domain rather than 24p, which breaks the 2:3 cadence needed to reverse 2:3 pulldown. When your TV tries to reverse the pulldown to recover progressive frames, it can't do so at those cuts so it blends the fields together and drops a different frame to compensate. 99% of people won't notice this, but there are a few who are sensitive to it. Nothing really that you can do about it.