I risked it and booked my flight back from Gatwick to Toronto on the morning of Friday 4th Feb, praying that they would have everything correct on my Confirmation of Permanent Residence form which luckily they did! My understanding is that if any name spellings or anything are incorrect then you have to return it to them for correction, which would mean that you obviously wouldn't be able to fly straight off...I think for most people there are no problems though so you should be fine!
My landing at Toronto Pearson was very smooth. My conversation with the Immigration Officer lasted no more than about 3 minutes. The only thing they asked me for was my passport and Confirmation of Permanent Residence form. He asked me how many Canadian dollars I had with me at the time (I only had about $20) but didn't need to see any bank statements or anything like that. He asked me for my address in Canada and my Canadian cell number. I should point out that I have been in Canada for almost 18 months already, as a visitor and on a work permit so I am already established in Canada in a lot of ways and I wasn't bringing anything over from the UK with me apart from the clothes that I'd taken for my 2 week visit. If you are bringing household possessions with you or are shipping things later then you need to complete a 'goods accompanying' and 'goods to follow' list. He told me where I needed to go to get my SIN and that was that! All very easy, and he said I would be getting my PR card in around 6 weeks time.
Hope that helps!