I actually prefer the 1 advancement per year of service (after the academy and cadet cruise) for Starfleet or equivalent, and 1 advancement per 6 months of extended combat (wartime). For civilians, I use a straight 1 per 2 years of work (after graduating from their school or apprenticeship).
I've always liked the variable "tours of duty" that FASA used, and ICON also included to some degree. It makes a character's background feel more like they've been in a semi-military organization.
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz