I've got an '07 RX400h AWD, California model, bought in 2009 with 40K miles, now have 86K miles. Overall I love this car; it's been good to me, and I have no interest in getting anything else. I live in Vancouver, BC, where we get a LOT of rain, and occasional icy/slushy/wet snow.
Here are my observations:
1) Front brake rotors were warped when I bought it. Replaced not long after with inexpensive non-OEM rotors... In the last 40,000 miles, they've developed a slight warp, but nothing worth fixing. The original owners lived at the top of a mountain, so when they went to work in the morning, the ICE would be running, and I generally get minimal brake regen when it's warming up.
2) Original Michelin tires lasted until now. I don't think the original owners ever replaced them, and I just replaced the Michelins last week. They were not impressive in the rain, and downright scary when there was black ice.
3) AWD: since the rear axle isn't mechanically connected to the front, it's not going to give you as good traction as a traditionally-equipped vehicle with a locking transfer case. That said, I've been quite happy with it. When the Michelins spin in the wet, a moment later the rear axle kicks in and it goes good.
AWD stories:
-Once I was heading up a mountain to go skiing, the road was wet, and it was snowing. The higher I got, the more the snow was sticking and it was nasty slippery slushy stuff. The traction control kicked in, and kept flashing at me as I leadfooted the car up the hill. The rear axle was running, and I was quite impressed at how stable the car felt, and how fast I was able to go up a steep hill in the slippery conditions. No complaints from me.
-Last winter we had a couple days of snowstorms. Vancouver's got tons of steep hills, and hardly any plows because it rarely snows here. The major streets were all gridlocked because it was crazy slippery. I drove home (12 mi) on side-streets (with steep hills). At one point, crossing Broadway, I was on a steep uphill (in Fairfiew Slopes, for those who know the city). There was a Hyundai SUV in front of me (I don't know if it was AWD). He kept trying to go, but his wheels kept slipping, so he was stuck on the hill. After getting frustrated waiting for him to go, I decided to pass him, and with occasional bits of wheelspin, I smoothly cruised past him. I was happy!
-AWD front wheel lockup: Vancouver's a rainy city, and the front Michelins slip frequently. If I'm heavy into the throttle, traction control applies ABS brakes to the slipping wheel. This causes a stiffening of the steering wheel which could be interpreted as a lockup. It most definitely is not, at least in my experience-- sterring gets stiffer than usual, but still steers, just with a bit more effort than usual.
4) It takes a solid 5 minutes to warm the engine up in the winter. Expect the ICE to run all that time, and your mileage will suck until the engine's warm.
5) Fuel economy: in 90% congested city driving, using the air cond all summer and defroster/heater all winter, I have averaged 9.33 Litres/100km over the last 43,677 miles. Converter says that's 25.2 MPG (US). That's based on the odometer plus my fuel receipts. This is better than my last car, a 4-cylinder manual transmission Honda Accord. Actually, it's the most fuel-efficient car I've ever owned.
6) Recalls: none to date have applied to my car.
7) What's gone wrong: the 12v lead acid battery was replaced once/twice by the previous owners, and I've replaced it once; it's undersized for the car's draws, and you can expect to come back to a dead car if you go on vacation for 3-4 weeks. The rubber boot on the parking brake pedal came off, and I replaced the front brake rotors (and pads) at 43K miles. And I just replaced the tires. My mechanic says I've still got 70% brake on the front pads, 50% on the rears (factory original pads).
8) My single biggest (and my only notable) complaint about the car is the undersized 12v battery. I don't know what Lexus was thinking. Mine failed about two years ago-- I'd left my headlights (and driver's door) open while filling the car with gas. There was enough juice to make all the accessories work, but not quite enough juice to get the car to flip on the power solenoid to the big hybrid batteries. So I was stuck on that cold, rainy evening until I found somebody who was willing to give me a jump. Previously I've had a couple of vacations where I get back home to find a car that won't start, for the same reason. Have to put a charger on it, or get a neighbour to give me a jump. He sure got a laugh out of jump-starting my two-year-old luxury car. All you need is enough volts to flip the solenoid to the hybrid battery.
Edit: because it's a tiny battery, it's cheap. A battery dealer installed a regular lead-acid battery (not the fancy OEM AGM battery) for $55, labour included. Still going strong after two years.
9) Cabin air filter: don't forget to replace it every year or so. My was gross when I replaced it at 40K miles.
10) I had my independent mechanic price out the cost of the timing belt job, which is due at 90K miles: $804, plus tax (Canadian dollars). Includes water pump, hydraulic adjuster, tensioner bearing, timing belt, long-life coolant, and labour. Parts all sourced from Toyota/Lexus.