With TiVo you get a trial period of about 2 weeks during which you don't need to subscribe - if you can combine this with a retailers refund policy you should be able to try a TiVo at no risk. Trust me though - once you've tried it for a few days you won't be taking it back!
The £200 lifetime subscription with TiVo is a good deal considering you will be quids in after 20 months... the reason TiVo offer the one-off payment is because they are a new company and needed the money upfront to fund future development - this isn't the situation with Sky so I would consider it highly unlikely they will offer a similar deal - basically there's no getting out of paying monthly subs to Rupert for as long as you have the service
TiVo are on the verge of releasing new software (v2.5.5 in the next couple of weeks or so) for the TiVo service. This adds many new features and is significantly better than the current shipping software. I understand new TiVo units will come with the new software installed but if you buy a unit with the old software the new software will download automatically a day or so after you first begin to use it.
On the hardware side Sky+ is more advanced than TiVo by having dual tuners, Dolby Digital 5.1 output and recording the MPEG datastream direct to hard disk, but it is a device designed exclusively to operate on a digital sattelite platform.
TiVo on the other hand supports all broadcast platforms, offers additional recording capacity by recording at varying qualities (Basic, Medium, High, Best in order of increasing quality) and the software is far more sophisticated than that in Sky+ (even the current version 1.5.2 - the new version 2.5.5 is streets ahead!)
Dual tuners in a TiVo would be nice but for me the picture quality is plenty good enough (from analogue cable I record mostly at Medium with films and sport in High or Best). DD5.1 is of little value to me - again it would be nice but I also have a DVD player for that!
PS. Why will the TiVo completely change your setup? It will completely change the way you watch TV but that's another matter...
