Mine came with an AUC warranty when I bought it (at 2 years old with 9,000 miles on the clock in November 2008), and had the engine replaced a little over a year later (at 23,000 miles) after it developed a misfire.
It had not been on track, it had not yet gone over 7000rpm in my ownership (as I was used to the 7200rpm limit in the M5), yet it still failed. Cause has still not been confirmed, but I gave up asking after a year.
I decided to continue/move to the BMW (Mondial) Insured Warranty, fully comp, £0 excess with breakdown cover. This was at a price of about £80 a month. The reason for taking out the monthly option vs the annual one, was that I was told the monthly premium would stay the same for as long as I kept it in force - whereas the annual one would be recalculated every year.
In total I've paid out about £4k in warranty premiums, and claimed over £15k for the engine, VANOS & diff. It doesn't include all the 'little' things that have been done over the last 5.5 years (wheel bearings, headlight washers, wiper relay, PDC sensors, brake caliper, etc.).
If I'd kept the premiums in my pocket and spent the cash when I needed to, I would not only be at least £11k down due to the cost vs savings, but I'd also be paying retail prices for parts & labour (even at an indy) for any of that work - which might be the difference between a £30/hour to Mondial, £50/hour at an indy, or £150/hour at a dealer, plus the loss of any 'special' pricing Mondial get on parts.
The downside (in cost and soul) is that I had to take it to BMW dealers for scheduled servicing - which was about twice a year at my current rate. But even that only meant a £500 or so 'loss' each year.
It's now done 80,000 miles in the 5.5 years since then, and does a couple of track days and Ring trips a year. It's not using any oil (that I can measure) in between it's 7,000 mile oil changes/services, but has left the odd drip on the drive which has been caused by seeping clutch slave cylinder, air-con compressor, diff, valve cover gasket, etc. and all have been (eventually) replaced/sorted under warranty or at a small cost to me.
About a year ago, when I was considering cancelling the warranty, I looked at the cost of re-starting it. I was paying about £80/month, but the new price (for a 60k mile car) would have been around £180/month.