I've swithced both, my high and low beams over to Sylvania Silverstars. There is a noticeable difference, it's almost comparable to some HIDs, in my opinion they are about 65-70% of the brightness you get out of Lexus HIDs, although no bulb replacement will be as good as true HID.
The one thing to be careful about when selecting these kind of bulbs is to go with a quality name (ie sylvannia) cheaper brands have higher chance of defect and lower quality and will blow on you after a couple of weeks. (this is speaking from experience)
The bulbs are a cheap alternative to HID and will have to do until I invest in a nice aftermarket HID upgrade kit!
:-)