Does anyone else think that the Xenon lights remind them too much of the Lexus than the Benz?

Sort of, especially the Lexus ES........

Sorry, but Xenon lights are something on a car that I just have no knowledge about. I know I'm getting the Bi-Xenon option (hey - they look cool! ), but to be quite honest I couldn't tell you what they're all about.

Are they just for when you have your brights on? Does it make the light extra-bright/white?

You could look around in the night, those cars w/HID
it's easy to tell, bright as "white" compared to the nearby
parking light, seems Yellow.
e.g W210,W208 are good examples to look around.

W209 equipped with clean lens, so it looks more focus.

I have to disagree. The Mercedes 03' CLK uses Projector lenses for their Xenons, while Lexus uses Reflective lenses. The big difference is that when you look at the merc's xenons, all the light is being projected out of the projector lens ( the thing that looks like a thick magnifying glass), The Lexus does not have projector lenses, the light beam is projected by using a reflective surface. The lexus setup is simular to a regular Halogen setup with the exception that HID bulbs are being used instead of Halogen bulbs.

Mercedes uses the the same type of reflective lenses on the C-Class but not the New CLK or E-Class. There is a big difference. Mercedes just started using projector lenses for their Xenons. Until recently I liked BMW and Audi Xenons better because they used projector lenses. Now Mercedes finally got with the program.

So you just use the Bi-Xenon's when you have your brights on? Still, nobody has really clarified for me what the purpose of them is or when you use them.

Bi-xenon means that low and high beam are of xenon.
Cars without bi-xenon will have low beam in xenon and high beam in halogen light.

The bi-xenon is kinda complicated to explain how it work
during day time. During night when you're driving with your low beam xenon on and let say someone cut in front of you and you got mad you flash high beam at him. your xenon low beam will have a flap inside that switch the angle of the light beam and turn it into high beam. At day time it's different cuz when you lights are not on, and let's say a idiot cut in front of you again and you got mad and flick couple flashes of high beam at that guy. but as we know when xenon lights are turn on for the first time it take about 60sec before it's really bright, therefore there's regular halogen high beam build in that does this so it can flash it's bright in an instance. (so at night with your xenon and high beam on you will have both xenon and halogen brights on at the same time) this is how bmw M3 bi-xeno works the CLK Bi-xenon should work the similar way.
kinda hard to explain in words but hope this helps.