Joseph,
As I’m sure you know, there are three nights a year when there is an “inyan” to stay up all night. Yom Kippur, Hoshana Rabba and Shavuos. The one with the least mekor is Shavuos. It is nevertheless the one which is most kept, possibly due to being the shortest night of those three. What I think charliehall means, is that of course many kedoshim stayed up on Shavuos, but the hamon am only caught on to this when it became more possible.
lowerourtuition11210, personally I always found Shavuos davening the most inspiring after a ‘whole’ night learninmg (max 2.5 hours in northern England), and stood all the way through and felt very uplifted. It is the only time everyone is there on time and davens together. This was all until I joined my current shul, where very very sadly, they plapper through the davening in very quick time. I sadly go home to sleep. But I happily come back for the ‘main’ minyan with my family.