I've had mine for like 3 months? So far no detectable dimming or glitches.
yah, it is 100x better than stock halogens. You know those older cars with factory xenons that don't have the dramatic purple blue shifting light kinda effect? They're kinda like that. Great bulbs. (and if you look at the lights closely, there's a visible blue tinge. cool!

)
I've yet to actually see my car in motion with the lights on. I'm reeeaaally curious as to how close the bulbs resemble real xenons.