One last snippet to come from today’s demo is that the new HD Sky+ box will have dedicated storage for what Sky calls a ‘push video-on-demand service.’ Apparently existing Sky+ boxes have this, but so far Sky hasn’t put it to use. The theory is that while you are sleeping Sky could automatically record one of its pay movie HD films on your hard drive. Then if you do decide to view it, and pay a few quid for the privilege, you only have to press play rather than go through an ordering process.
Sky's Director of Customer Products and Services, Brian Sullivan also added that he thought it might be used to push popular programmes to a hard drive. So for example you might not need to even put Little Britain on series link, it will be automatically be pushed to your hard drive. It’s an intriguing technology and it’ll be fascinating to see what Sky does with it, and how consumers react to having extra programmes arrive on their hard disk.

The BBC and Tivo have already done this in the past and received many complaints over it (some people found their Tivo was unexpectedly full as a result).
Here is a quote regarding this.
"1000's of TiVo users were unhappy to find that the BBC had hijacked their TiVo box by auto recording a show without their consent.
The BBC used a function of the TiVo recorder that offers viewers recording suggestions or automatically record a viewer's favourite programmes. TiVo owners woke up to find that a recording of Dossa and Joe had been made overnight.
Users accessing the TiVo saw a new item "Must See from the BBC Dosser and Jo" as part of an "advanced content" feature.
The BBC has been collaborating with TiVo for about 2 years. The BBC is claimed to have taken the attitude that viewers were not forced to watch the programme that was recorded, just given the choice.
Although the BBC admitted that this post watershed show should not have been used to test the service.
Reports are already suggesting the ploy is an own goal for TiVo which has failed to meet sales expectations in the US and UK."
As your article indicates, Sky now reserve a substantial portion of the disk space on Sky+ boxes for this facility (reducing the capacity potentially available for customers own use).
I am opposed to this behaviour, such a move should be up to the choice of the customer and not forced on them by Sky. Sky should also give the customer some input at least as to WHAT is downloaded (e.g. last 7 days of certain programs based on customers viewing habits).
John's comments are correct and quite a few TiVo customers were worried about that and unhappy about the idea of losing control of their TiVo's (myself included).
It should be pointed out however, that it didn't actually 'fill up your TiVo' preventing other (scheduled) programmes being recorded. The programmes were recorded if if there was free space available and as with all TiVo suggestions, deleted by the TiVo automatically as needed to make space for scheduled programmes (I seem to recall it was even pre-marked with a 'ready for deletion' flag so the TiVo would prioritise it for deletion, in preference to other programmes).
I think the biggest problem was the way it was handled - the content was not clearly marked as being a 'special suggestion' or promotion, it just appeared as if it was a regular TiVo suggestion, based on user preferences - as if it was something that you might genuinely have wanted to watch based on your viewing habits, which of course it wasn't. The choice of show certainly didn't help either.
I think the key to rolling out something like this out is clear communication and a way for customers to disable 'suggested recordings', as you can with TiVo's. As Sky+ systems don't have suggestions already, there isn't any chance of confusion in the way there was with TiVo units.
The issue of reserving disk space could prove to be a contentious issue though, particularly with HD content being sure to require significant amounts of storage space (it's possible that even with larger disks, users could see an effective reduction in the amount of hours worth of TV they can store if they record a significant amount of HD content, though that will obviously depend on the storage capacity of new HD Sky+ units).