If you can watch one channel while two others are recording, then the DVR must have at least three tuners. I read in an article a while back that the X1 DVR supposedly has six tuners, but I haven't seen that anywhere else (info about these boxes is very limited), which is why I asked how many tuners are actually there.
Nice to know the 5-minute jumps are there. That's one thing I-Guide has that I with other platforms offered (we have both Comcast and DirecTV, and DirecTV's boxes don't have anything like that).
I still would like to know if there's any form of 30-second skip or scan. Is there a button on the remote that does this? I understand it is an RF remote, so it's unlikely the function can be programmed like you can with I-Guide. It would therefore have to be a function already on the remote. DirecTV's remotes have the function built-in, but by default it is a "scan" function which fast-forwards for 30 seconds instead of an instant skip (though there is a way to change the behavior with a special keyword search).
I believe I found the answer to the hard drive size. It is apparently 500 GB (same as the newer DCX3501 / RNG200N boxes from Motorola). The upcoming cloud storage capability should help (depending on exactly how it works), but Comcast is notoriously slow at rolling out new features, so I wouldn't hold my breath for it.
User error. Replace user.