I flipped on my (Philips DSR6000R01) DirecTiVo the other day and immediately noticed the remote signal was flaking. Commands were received slowly or not at all, and the LED lights on the front of the main unit were blinking like crazy—probably about 6-10 times a second. I figured the remote's batteries had croaked mid-click, causing some kind of fatal IR loop, so I popped in two fresh AAs and rebooted the TiVo twice. No dice; same problems.
After five fruitless phone calls, $19.95 of pay-per-incident support bought me the observation that I "might have a power supply issue," so I should just send the unit in for an official look-see. Based on what I'd heard from friends with similar problems, though, the official Philips "diagnosis" was frequently "Go buy a new unit," so I opted for a more lo-fi solution.
On a lark, I stuck my finger over the main unit's IR eye, and the blinking stopped immediately. Moreover, I noticed that if I covered all but a very tiny corner of the eye, the signal was received flawlessly. So, I taped a piece of paper over most of the eye, and, after a couple small adjustments, the unit worked flawlessly, even on signals from far across the room. A week later, it's still working great (knock wood).