Yesterday, Humax announced new 80Gb and 250Gb TiVo, the top one offering up to 300hrs of storage at the lowest quality. You can buy upgrade kits to do pretty much the same and I suspect the ~$600 unit will likely cut into sales by TiVo upgrade kit folks.
The good news from all this is that the Series 2 operating system in these Humax units is definitely supporting large disks. The linux kernel used by TiVo could only see a maximum of 137Gb in any single hard drive. If you stuffed a 160Gb, 250Gb, or larger drive into a TiVo, you'd only see 137Gb of it.
Until recently, the only way to get large drive support in a TiVo was to hack in a LBA48 sensing kernel, like this hack mentioned previously on PVRblog. When the HDTV TiVos were announced and released, they too came with 250Gb drives and the TiVo hacker community knew it was only a matter of time before new TiVo OS upgrades would allow for large disks.
Humax is planning to release their TiVos later this month that feature a single 250Gb, and word on the street is that both these new units and the Pioneer DVD burning TiVos (as well as all new TiVos, eventually) are running a new 5.x version of the TiVo operating system, complete with a linux kernel update and large disk support, which is good news for everyone. No longer will upgrades require more than one disk to get more than 160 hours of storage.