Do you think "marathon fever" is here to stay or is it another fad like badminton, bowling, pearl shakes and shawarmas?

Fad. Definitely fad.
Cripes! As a kid, running WAS already an activity we loved. Now it takes "an event" for people to do it.

Probably babalik ang street parties/rave.

Or maybe ang Twitter/Plurk based events.

Ask me anything