Re: Which DOCTYPE do you use?
It really depends on the project for me. It doesn't help that you develop a client's site with the Strict DOCTYPE and then if they make alterations to the copy and manually enter erroneous HTML (or unencoded ampersands, for instance) the site will no longer validate. Hence I generally tend to design and develop clients' sites in Strict, but change the DOCTYPE to Transitional before it goes live. Once again though, it depends largely on the project.
For personal sites I'll always use either HTML 4.01 Strict or XHTML 1.0 Strict since it teaches me coding discipline. You can't be lazy and leave a tag unclosed or nest tags improperly, et cetera.