On my N810, I can switch it off in the default browser as a what seems to be per-process setting. It takes three touches to toggle it from the main browsing screen. I don't know what it is on the N900, but I really doubt they'd downgrade it to a compile option.
Other browsers available on the platform might have different functionalities — in particular, the alpha/beta of Opera Mobile has click-to-Flash—like functionality.
If so, that is great. I still don't miss Flash on my iPhone, and definately want to still keep on missing it.