For me, it is the smell of an old cab that immediately sends me back 25 years. It is a not a particularly pleasant smell, but once that monitor warms up, it smells just like all the arcades I grew up in.
In high school, the school bus home left 1hr after school let out and there was an arcade right next door. From 1983-1987, I literally spent 1 hr of every single school day in the arcade (usually broke and mooching quarters). And when I wasn't there, I was in the back game room of the donut shop in my local suburban strip mall.
Having spent a good part of my formative years playing arcade and pinball games, it is no wonder that 25 years later I have a strong sentimental attachment to these machines.