Today I had a bit of a crack at Commerce coupons.
They actually work really well! As with anything commerce related, the whole thing is so well thought out that it takes a few minutes before you can catch up with their trail of thought, but after a while of battling through rules and workflows I found myself with a couple of basic coupons working. And only then did I discover commerce_coupon_pct and commerce_coupon_fixed_amount. Looking at the code for these modules it probably would have taken 5 minutes to work out what took an hour without them.
ALWAYS remember Drupal rule number 34... (There's a module for that!)
But all things said and done Commerce Coupons in combination with Rules give you A LOT of flexibility in terms of saving customers money. Now I just need to find out what my client actually wants coupons to do and then to 'attempt' to find a fool proof way for them to implement new coupons.
Another fun day with Drupal over...