Meta Description / Keywords Helpful?

Looked and looked, can't find the answer...

[whoisgregg]

Is there any point in adding the metatags for description or keywords to affect Adsense ad targeting? For a primarily image content site, is this a reasonable alternative to adding the paragraph describing the current page?

From the past threads I've researched at WW, I can't tell if people are recommending adding these tags because it's part of their "good things to always do" checklist or because it actually matters for Adsense targeting.

Knowing the general situation with these tags, I've chosen to not use them at all -- is this a mistake if I start participating in Adsense? Thanks, all! :)

[swoop]

Will AdSense have some pertinent text at your image site upon which to base its targeting? If not, you may not be happy with the ads it selects to show.

[whoisgregg]

Can I put about 30 words into the meta keywords and meta description tags to affect the ad targeting? Not keyword stuffing, but putting legitimate and accurate info in those tags? Or does Mediapartners bot basically ignore the metatags just like googlebot ignores them?

I know I could put the text on the page itself but I am exploring alternatives that will not affect my current layout. :)