What ratio of [senior] developers to testers do people think is best?
Obviously this will depend partly on development/maintenance throughput, but is there a rule-of-thumb that a new company/project might work from?
Also, would you use 'pure' testers, or would you combine testing with other roles (e.g. documentation, user training, etc)?
Obviously, answers may depend on company strategy / development models used, so please specify if you're answering in general, or if for a specific style of product/release, and so on.
Joel makes a good argument for 1 tester for every 2 engineers, as well as covering the excuses people use for not having those testers.