I generally try and make sure that my releases are at least XHTML 1.0 Transitional, but there are always one or two that get through because they have been coded and released that quickly that I completely forget about checking it first. I do try and go back to them and check them over at a later date to validate them, but I know that a number of my earlier releases are not W3C compliant. That's progression and learning for you though. ;)