Hi everyone!
I use XHTML 1.1 on my site and also use Adsense to place ads. Their referrals and ads for content ads work well and can be validated, but their search service creates problems. You see, the form which they provide does not quite validate with XHTML 1.1 and so the website becomes Invalid. And that's why i decided not to use Adsense search.
With many people switching over to XHTML 1.0 and maybe above also, don't you think that google should update its ad code so everyone can use it? And, we are further limited by the fact that we cannot alter the ads our selves.