I have a 2004 RX330 so there's much I can tell you. First, I was told by two former Lexus mechanics that the timing belt is NOT interference. Supposedly, I had mine changed at 90K, along with the water pump by a nonLexus mechanic in Chantilly, VA. Another former longtime Lexus mechanic recently changed the drive belts and told me it looked as if my timing belt was never changed because the bolts that would need to be removed for access to the belt had no impressions in them (and removing them would leave impressions). When I looked at the itemized receipt from the 90K maintenance, lo and behold, no timing belt was listed under parts in spite of the job being listed as one the jobs to complete. Sadly, there are lots of disreputable mechanics.
IF the belt was never replaced, that means mine has lasted over 150K miles. I plan to trade in the car soon, so if it breaks, I'll have it towed.
Here's something interesting. I'm shopping for a newer RX and if you look at the 2011 maintenance schedule on the Lexus website, timing belt isnt even listed. Is it "lifetime"? Is it one of those things that doesn't need replacing till it leaks/breaks/look worn during an inspection? I can tell you, I still have the original shocks on my '04 and have been told that they don't need to be replaced unless leaking.