Only done just over 2,000 miles but the handling doesn't feel the same as when new.On smooth A roads it doesnt feel that different from new but on the minor back roads it doesn't have the 'planted' feel that it did when new and the steering doesn't feel as 'tight'.

Checked the tyres and they are all okay and correct pressure

Mine never felt 'planted' even when new as it seemed very skittish at speed and would also try and follow every deviation in the road surface. I took the car to Tony at WIM and it looks as if Lexus have repeated similar errors in the set up as the IS200/300. Anyway. some minor adjustments later (there is only front and rear toe adjustment) the car drives as it should, and having been back for two or three 'fine tunes' the settings have been completely stable with minimum tyre wear even across the width of the tyres.

16000 miles in and still totally stable and "new". No tweaks at all...

You might expect some tram lining with wide low profile tyres

When you say you checked the tyre pressure , what pressures are they?

Would you? The tram lining occurred with my OEM 17" wheels and tyres. WIM first made minor adjustments with these fitted and the skittishness and tramlining went away. About a month later we lowered the car and again made minor adjustments to the front and rear toe to reset the new lower positions and the slightly increased negative camber, again with the OEM 17" wheels and tyres.
Around 2000 miles after the lowering I fitted 19" wheels (8.5" front & 9.5" rears) with, of course, much lower profile tyres and returned to WIM for a fine tune (no alterations necessary)...guess what, still no tramlining and the car is still very well 'planted'.

Tango
What toe settings do you use to prevent tramlining?

Can only tell you my current settings which I believe are 13' inclusive toe-in on the front and 29' inclusive toe-out on the rear.
Don't forget I have more negative camber on both front and rear than is allowed for on the OEM settings (including the IS350 & Sport) due to the front being lowered 1.4" and the rear by 1". There is no camber adjustment for the second generation IS.
No doubt Tony will come along and correct me on the settings if my memory has failed me.

I'm not saying cos your set-up was custom

Hoi...that's not the caring, sharing Doc of Geometry from Christmas past. Bah humbug.... (I think you'll find my memory is pretty reliable)

It's not

Doh.... sorry Bluey

I can't get my head around the fact that you spend a lot of money for your 'brand new' Lexus and you get shoddy handling.
I can speak from personal experience with several 'Brand New' Lexus'es. I know it's easy for someone to say '...well just take it back and they will put it on the ramps', it shouldn't be like this from NEW surely??

Are BMW, JAG & AUDI like this too???

Tango
Do you take this machine on track, or just for enjoyment?

Does anyone know what 'standard' settings would be best for straight line stability and good tyre wear, whilst still balancing effective turn in with minimal understeer? I'm mainly after tyre longevity but occasionally enjoy a run on windy roads.

Yes they are.

Ditto ...especially the windy road bit, and it does that superbly. Have also explored the limits of the handling on the perimeter track and main tarmac runways of my club airfield...it can be a tad tail happy, especially in the wet, but nothing too unpredictable or correctable..haven't spun it, not yet anyway.
I've got, but yet to fit the IS350 calipers and discs upgrade. Made the decision as the original 250 spec feels a bit on the limit when pushing hard. They'll stop you OK, but the pads and discs won't last too long (the dust produced is incredible).

The toe out on the rear will certainly make it more tail happy rather than the generic toe in, understeer option. I also found to have some toe out on the front gave better turn in, but will increase the tramlining from the front.