The incredibly unwieldily named blog Virgin Media High Definition & TiVo Services posted a 17 point comparison between the new Virgin Media TiVo and their old V+ box. TiVo won, handily – 15 to 2. The only two points TiVo lost on are speed:
Speed. TIvo’s biggest problem is that it can be sluggish, especially compared to the V+ – but it’s not dramatic and it is more often than not faster. Searching TV on demand is significantly faster for example.
It sounds like it didn’t lose that by much, and prevails in some cases. And reliability:
Reliability. By far the biggest issue I have with the Tivo is that if your internet connection is down, then yoru Tivo loses significant media – such as the discovery bar, TV Guide updates and programme info – and it errors and throws you out of certain options. A pain in the backside. V+ was far simpler than that and thus didn’t suffer network outages.
I’d argue this one. TiVo has more features, and many of those features rely on the broadband connection, and if your broadband is out of course they won’t work. The old V+ didn’t have comparable features, and if something isn’t there at all it is hard for it to fail. 
Give the whole thing a read.
