I broke down and picked up a new Plus unit today from Best Buy. I hold you all personally responsible for triggering the UMF on this new TiVo.
Install, Set-up & Pairing went as smoothly as possible, harvesting the M-Card from my XL4 unit. 6 tuners right out of the blocks.
Only delay is MRS functionality between the Plus and the XL4. TiVo reports "up-to" 72 hours before the media access key is released to the new unit. How odd; seems like should be instantaneous. I would have liked to move over my XL4 SPs and recordings this afternoon - but whatever.
UI looks and performs great! Lag was my only complaint from the S2s, S3 and XL4. Looks like a very nice improvement!