Do modules load randomly during boot?

[Michael S. Jessop]

I only ask because sometimes the system boots right up, quickly and
flawlessly.  At other times it will sit at "loading modules..." for a) a
long time (like, I left my house at 2:00 and got back at 10:30 and it
was still sitting there) or b) several minutes.

In scenario b, I get impatient and begin wiggling my mouse and hitting
keys on the keyboard.  Not a controlled test.  :)

Anyway, just wondering what might cause this inconsistency.

Mike