Infiniti has been the luxury arena's sales growth record-setter for more months than I can count. The G35 has multiplied like mosquitoes, the new M is doing 1,100% better than the last, and for the "bionic cheetah" FX it's looking like a victorious catfight. That's what happens when you boldly invade three fiercely competitive vehicle segments, look every competitor in the eye, and overpower and underprice the lot of them. Works every time.As the sole survivor of Infiniti's original cast, the Q45 has been around long enough to know that it wasn't always this way. It has definitely seen darker days; times like 1990 probably conjure up depressing memories of 12,000 annual unit sales. 15 years later, the Q45 is still the top dog, and it even learned some new tricks for 2005. In this enlightened era of redefined luxury, does it still have what it takes to stay atop the Infiniti heap?