Bought a gamebit on fleaBay and opened the ol' GC up. Turned the potensiometer ever so slightly counter-clockwise and VOILA - the laser lens is apparently recalibrated. Now, disks are being read again at startup (no more DRE's!). Used the instructions found here and here.

Here's the location of the potensiometer on the back of the disc circuit board (circled in red):


If you are having problems with your discs not being read at startup (the GC will tell you that there is no disc in the drive), you really should try calibrating the lens.

Good luck!