The Pioneer DVR-520HS doesn't have TIVO; the Pioneer DVR-810HS does. As with most (all?) DVD recorders incorporating TIVO, you will not be able to make edits to your programs recorded with the TIVO feature. I have the Pio 420HS (identical to the 520 minus DV input) and really like it. Easy to make edits through Playlists and burn to DVD.
I just love my Humax TiVo DVD recorder. It's soooo easy to use and I am pleased with the picture quality. Like Elizabeth said, with any TiVo/DVD recorder combo, you are unable to edit the programs. Best of all, I was able to snag it for $199 after a $100 rebate. Right now, Sam's Club has it for $399 minus a $100 rebate.
I would call Pioneer back and question them again about this unit having "integrated TiVo". There is no mention of it on their web site. And, I just searched through the Owner's Manual, online, and "TiVo" is not mentioned at all. My bet is that this unit does not have TiVo.