SMC Methanol/Water Injection kit on my 06 wrxSTI. Pushing 25 PSI and 365 AWD WHP (on a mustang dyno)
http://img79.imageshack.us/img79/4529/picture045zv0.jpg
40k miles racing and street with zero problems to date. Just make sure your methanol tank is always full or you will blow your engine under WOT.