Well ive had her a little over a year now and its been an absolute dream. Motd 3 weeks ago and sailed through with no advisories. Not a single thing has misbehaved with the exception of one of the rear number plate lights. Also she uses a little oil but i make sure i keep a close on eye it and live with. Not sure if this is normal as uses about half a litre every thousand miles or so. This is my 2nd X5 so im well aware just how the issues can stack up at times and given all the problems the previous owner had with her im feeling very lucky and happy.
I bought this from a forum member and he had been really unlucky with her having most of the common faults such as panroof, compressor and both the bag struts as well as a brand new gearbox installed by BMW last Feb during his ownership. When i went to view he showed me all the receipts for the work and i could have kept the BMW warranty running but given all the work done i elected to take a punt and saved the dosh as my contingency fund which ive now just stopped as theres now a nice lump for future probs. Tempting fate here i know so watch the faults roll in.
Ive not done a lot of miles in the last year just 6k which is why I wanted a petrol 4.8, I know you hear of lots of horror stories but in my experience anyone contemplating one of these I would say definately go for it. This was a 70k when new and together with all its extras and the immense engine noise i absolutely love it. Just make sure youve got a few quid tucked away to one side when they go wrong.
I would definitely buy another X5. If you do your research you can factor in these costs. Like you said re the warranty you took a punt as I did also and didn't regret it. 
