You sign up for a free account and then you can run the Analyzer and it will give you a score and some basic assessments of what you can do to move your score upwards.

I might write a full article on the SEO Tools sometime soon, but wanted to share this info right away.

That said, it’s not always practical (and doesn’t always make a big difference) to eliminate all errors. In the cases you gave, I probably wouldn’t worry overmuch about the embed error (these are pretty common with embedding videos using the provided code and don’t seem to make a notable difference to the search engines).

That said, I’d fix the double alt attributes right away, because the search engines do place value on the content of alt attributes, and having two in one tag is likely to confuse things. You’re basically missing out on an opportunity to tell Google what you’re all about.

Bottom line, the Validator isn’t a be-all, end-all kind of check… it’s just an indicator of general attention to code detail.

With WordPress or TypePad, that’s usually not the case, because they both have a way to reuse pieces of code (WordPress calls them Widgets; TypePad has TypeLists).