One account (well, a main account and an alt I created after I was unjustly banned from my preferred CS:S server), but since I bought stuff across a few different store regions, I have a few different coin balances as coins don't transfer across currencies like, say, Steam Wallet funds do. The amount of coins you can earn per x currency units spent, the number of currency units you need to spend to earn coins, and the discount you can acquire with the coins all vary currency to currency, so each one has its own coin pool.