I put together this info and plan to submit it to scoobymods, and if it's deemed FAQ-worthy, the FAQ here. It seems like questions about this come up a lot. It's specific to TS and RS but would probably be useful to WRX owners wanting to upgrade their lights.

Hella 500 Install:
http://users.sisna.com/ignatius/subaru/mods/fogs

Let me know what you think, and I'll try to improve or change things if necessary. Thanks.

i know this is last year...but...is the bottom of the light actually on the bumper?? does it vibrate around a lot?

:lol:

Holy crap, I haven't visited this forum in months, and what are the odds that today there's a question for me here. Cool.

Th light is mounted via the stud going through the hole drilled behind the light, and it's pretty secure. The bottom of the light touches the bumper, I guess you could say that, but it's not loose, so it moves with the car and not independently, so no, it doesn't flicker or vibrate. At least we haven't noticed any problems, but then again it doesn't spend a lot of time on rough bumpy roads at night. The fogs work really well, great for lighting up dark roads and providing more illumination to the sides of the road, esp. when it's twisty.

Hope this answers your question!

Steve