Are you using tools like SEOQuake or
SEO for Firefox to look at the analytics of these directories?
If they're high authority ones like BlogExplosion, SEOMoz, Technorati, they're definitely worth submitting too. (although these don't require a reciprocal link).
the directories which require reciprocal links typically are new directories and the owners are trying to build them up.
I'd also look at the types of blogs that are listed in these directories.
If they're made-for-adsense (MFA) blogs or scraped content blogs, I'd avoid them like the plague.
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An alternative is to setup a "Links" or "Partners" page and put the buttons on these pages. That way if you leak Google PageRank (for
SEO ranking purposes), you "leak" it only from one page, rather than putting in on your blog template (probably a sidebar) and leaking
PR value from EVERY page.
Hope these tips help.