I've been using the 540HX for a few weeks now and thought I'd post my thoughts on it, its impressed my alot more than the Sony 710 I own.
The Good :
Fast transfers from HDD-DVD, DVD-HDD (even while a 'real time' recording is taking place on the HDD something the 710 can't do)
The ability to edit while recording (again something the 710 can't do)
Digital tuner quality, the list could go on...

The Bad:

The remote....it looks like a kids toy and certain buttons (fast forward etc.,.) being hid under the cover makes it a hassle when editing, I've started to use my Pioneer 320 remote for editing as I prefer to have all the buttons on show (I also don't like the 'shift' button)
Lack of features such as being unable to extend a timer recording while performing the timer recording (the 320 and Sony 710 allow this), unable to adjust the MN recording quality via the timer schedule screen, and a couple of other features, no XP+ mode and -RW VR chase play (HDD only) like previous models have been able to do, I've asked Pioneer about these, they gave no reason other than its a new model and theres no reason why it should have these features, can anyone else tell me?

Overall its an excellent recorder which will no doubt only be bettered by the next model.

Can't you cancel the timer and go to manual control, then set an OTR countdown to extend the recording time?

The thing with XP+ was that it was a bit of a white elephant: it's too high a bitrate to be copied to DVD without re-encoding. It's only possible use is if you were editing DV tape and want to record back to DV tape.

Chase play isn't too useful on DVD; I've certainly never used it. I guess this is a lesson that newer doesn't always mean its features will be a superset of older recorders. Some things could be dropped (like the chapter mark button)

Overall, I'm glad I've got a 530 then! Definatley sounds like they have taken a few backwards step.

I had my second instance of being unable to extend a timer recording when I wanted too tonight, the match on ITV1 was running late so as a result I had to make another timer recording that would overlap the original not an ideal solution as it missed part of the footage during the changeover but its the only workaround that I know of, its annoying to think that such a simply feature couldn't be included in a new model when it appeared in older models. Anyone think Pioneer might release a firmware fix?

Come to think of it I don't think you can extend a recording during an event. Have you tried pressing the record button a couple of times to see If that works ala manual recording?