I just got a letter from Comcast telling me that they are transitioning to MPEG4. Luckily I have a TiVo HD, TiVo Premiere, and a new 500 GB TiVo Bolt (still unopened) that handles MPEG4. I am planning on upgrading my 500 GB Bolt with a new internal drive and am now wondering with the switch to MPEG4 this means that the recording capacity of 500 GB should now be increased from the current 75 HD hours to something more. Does any one know what the improvement should be? Will 500 GB now handle 150 HD hours in MPEG4 format? If the improvement is great enough, I might not need to upgrade my Bolt's hard drive.