I guess I've been pretty lucky with my '84 240 (luck, and my careful, Brickboard-inspired maintenance). This car (nor my two '93s) never failed NJ's emission inspection (the dynamometer on-roller kind) yet, but I was worried (as always). But, she passed again, this morning! Yay!
Since the state has been giving a page to owners with the actual numbers (last three 2-year cycles), I've kept a record:

gas---- Limits-- 2004--- 2006--- 2008---
Mileage--------- 193,289 215,925 225,635
NOx---- 1227---- 33----- 181---- 248
HC----- 162----- 27----- 21----- 36
CO----- 0.91---- 0.02--- 0.12--- 0.15
CO2------------- 14.7--- 15.0--- 14.4

The past couple of years, I've mainly used her as a winter "beater", since getting my more favored '93 which I use for the spring-to-fall seasons, keeping it "in storage" over the salty winter months); the only time I use it in the summer is to tow my sailboat (since I don't want to get my '93's upholstery wet!); that's why my mileage has halved over these intervals.

I celebrated today's "pass" by installing IPD's wagon (though it's a sedan) overload coils, because lately she's been sagging under my sailboat trailer's tongue weight -- I bought the coils in advance, just in case :-).

Not bad for a 24-yr-old car! Volvo runs on and on!!!