In my location I just never come across that problem.
You can't compare it to the Garmin really, Garmin is in the business of just designing navigation systems...Lexus' system is designed alongside the other electronics in the vehicle, its all done on a overall budget. Garmin's GPS R&D is much more vast than Toyotas, because Garmin is selling much more GPS units and thats the sole focus of their R&D efforts. You need to compare the Lexus system to the systems offered by other carmakers as built-in. Its pretty comparable. The data all comes from the same source too...so if you have a navigation routing issue in the Lexus...you likely will in an Acura, a BMW, etc as well.
For 95% of the motoring public, the system is excellent. For GPS aficionados and those who are used to systems developed by stand alone GPS manufacturers like Garmin or TomTom, not so much.
Think about it this way, compare an old Motorola Q to a Blackberry. Blackberry had perfected the smart phone circa the mid 2000s. The Q by comparison was clunky and poorly designed. Why? Because all of Blackberry's R&D went into designing the Blackberry, when only a small portion of Motorola's did.
Now Motorola is using the Android platform so they don't really have that issue.
Eventually car companies will start contracting with Garmin and TomTom to produce their systems I have a feeling...