I have a 5504 and it has a function called Show|Nav that allows you to skip forward and backward in "segments." It seems to have the same functionality as CA, working about 75% of the time skipping commercial breaks. Just press the right or left arrow on the remote while watching a recorded show.

Yeah, it's pretty much manual CA. CA did the skip automatically and they retagged this feature as Show Nav in the 55xx series. So, it doesn't really navigate to key chapters in the show, it just goes to the next section where it detected a commercial break.

Sho|Nav looks for blackout points. I think it looks for a certian level of IRE black, but I'm not sure what level or for what duration. This is why sometimes it misses commercial breaks or can go to a segment in the middle of a show (like Law & Order or older shows). It also tends not to function well if you're watching a buffer of a currently recording show.
-GtG-

I have a 20XX series, which I upgraded to an 80 hr hd recently. I found that you can go ahead (or back) on a recorded show a certain # of minutes, instead of just 30 secs forward or 7 secs back. You simply just press the # of mins you want it to go foward, then press "30 second skip" and it will advance (or go back) that many mins. It works great. It will not work on a paused show, though.

For the 55XX, there are hacks which allow you to turn internet sharing AND commercial skip back on.

Now, when ReplayTV does the automatic program schedule update and software update, it will re-disable commercial advance on hacked ReplayTV's. You will have to go back in and re-hack after every update (which is difficult to avoid, but i believe someone created a .dll file to prevent this, called "NoUpdateDll" i think). Good luck.