I had my Cambelt done at Lexus as I believe it's such an important part I didn't want to take any risks but thats just me. I'm not going to say its more important to go to the dealer for your major stuff as most will say don't bother and go to an independent.
Anyway, dealer was £50 dearer than my local garage who I do trust for the cambelt, but they admitted they hadn't worked on many IS200's so I went to the dealer. Lexus also stamp your engine cover with the date, mileage and initials of the mechanic who changed the belt which I liked. Excellent service, nice coffee, paper, sky sports news etc :)
I also had the 100k/10 year service done at Lexus. They were initially £120 dearer than my local for the same work but I haggled a little and got them down by £70. Again superb service. Also I had the 3 aux belts changed at Lexus for £55. My local garage wanted £80.
I've also struck up quite a good relationship with the dealer as I've bought brake callipers, spark plugs and new keys through their parts department. I've found I get great treatment the more business I put their way as they let me test drive a GS250 even tho they knew I couldn't afford it and while I was on said test drive they did a wheel balance on all weels for £15 and washed my car inside and out. Ok it was the 28th Dec and I was the only customer for miles and just forked out £200 for a brake calliper but still....
Most people are put off by main dealers as their scared of paying over the odds but I've found Lexus will negotiate just like any other business.
So that's just my experience and I've been very happy with Lexus and will continue to use them for servicing. I know the stamp in the book adds no value to my car at 12 years old but I don't go there for that. I would think most on here with similar age cars to mine will think I'm mad