I just recently constructed a summary spreadsheet from 15 years of playing VP. I was fairly surprised at these figures:
Source % of total
cashback 33%
coupons/freeplay 26%
drawings 10.6%
gift cards 5.1%
Looks like 75% of my VP profit came from these 4 categories! I'm pretty sure that during the last year or two, these same categories contributed almost 100% of profit.
I actually started playing about 1990, but don't have good records of the early years.
G'luck all,
Gamb00ler
P.S. I counted gift cards at full face value.