Michael,
First of all, thak you for taking the bull by the horns and doing something to address this issue.
i have bought an RX300 SE in march 05, and I have the same problem. As LexusJohn pointed out, i gently press the accelerator to avoid the jump, but sometimes, it happens regardless.
I also had a GS (Aristo) and did not experience this, and have an SC430 and don't experience the problem either.
I believe it is something specific to the RX.
Count me in as well.