We thought in the past that the keyword limit at adCenter was about 40-50 thousand keywords per account. We now know that the limit is 100,000 keywords and 20 ads per order. Of course, like last time, you are allowed to request up to "3 account per credit card, which may include one or more campaigns and one or more orders." You may also request an increase to the 100,000 keyword limit. Here is an email posted in WebmasterWorld from a Microsoft adCenter representative.
At this time, Microsoft adCenter will allow 3 account per credit card, which may include one or more campaigns and one or more orders. The limit for keywords is 100,000.00 and 20 ads per order. You may submit a request to increase the keyword limit. To do this, I will need the following information:
1. Customer name and account number
2. Customer service level (Standard, Select or Premium)
3. Requested limit
4. Business justification for request
Once we have received your request, it will be looked into and will take up to and including 7 business days to complete.
You also may create another account using the same credit card. You would then have an additional 3 accounts to use and create additional campaigns and orders. You would still have a keyword limit of 100,000.00 in total for this new account.
Forum discussion at WebmasterWorld.