There is a lot of misinformation and confusion on multiple adword accounts, on the web.
This year we wanted to provide our customers with a better user experience, and was woried about multiple accounts and the double serving policy.
I have extensive discussions with Google over this, and I even taped a conversation I had with my adwords advisor, so I have proof, if they ever try to ban me. This is basically what our advisor told me; which I have put in my own words:
It is perfectly fine for a corporation to have multiple accounts. Our adwords advisor has said this on several occasions. As long as you do not violate the double serving policy, its all fine.
In additon if you have multiple businesses in which you have controlling interest, and try to double server this way, you will also be violating the double serving policy.
I'm not sure what the policy is for individuals, but I assume it would be the same for a corporation.
But the driving factor behind the number of accounts, is not the number of accounts itself but the double serving policy.
The policy should read:
For each Business (or multiple business's in which you have controling interest) - One account per unique product brand.
For too long, we have been puting the cart before the horse. Instead of asking yourself, will I be ban if I have multiple accounts; ask yourself if having multiple accounts will lead to double serving (intentionally or unintentionaly). If the answer is no, then it is fine to have multiple accounts.
Unless you have a new account, I would not touch adwords vouchers.
They are only ever valid with a new account. This gets very confusing when G send them out to existing Adsense publishers as they are restricted to a single account and don't realise that Adwords is different.