If I recall correctly the HR20 will overlap as long as the recordings are on the same channel or am I mistaken?
Well, technically, two shows on the same channel can't possibly overlap.
I think what Billy might be referring to is the feature that Tivo should have had from day one, which is if the tuner is not scheduled elsewhere, it takes the output from a single tuner, and records just a few seconds more than the scheduled time, typically at the head and at the tail. If two shows are back to back on the same channel and you record them both, when you play them back, you will get the last few seconds of the first recording also duplicated on the first few seconds of the second recording (although the HR2x cleverly cues it to where the overlap ends--you may have to rewind to see it).
IOW, it takes the tuner output and for a short overlap period funnels that into both recordings--the head of one overlaps the tail of the other, and for that short time one tuner contributes content to both recordings.
What this means is that if you have "seamless" broadcasts, such as "How Hard I Banged Your Mother" blending directly into "Two and a Half Men" (with no commercials in between) you will get all of both shows. Sheer genius! (of course no PVR can predict how accurately the broadcast time will match the Tribune/EPG time that they CLAIM the show will fit into. Blame that on the broadcasters).
Compare this to Tivo and every other of the dozen PVR's I've owned, every one of which truncated about 15 seconds between the end of the first recording while it ramped up to start the second recording, which I always found supremely annoying. Until now, that is.