I'm laying out the structure of my page like this:
<hgroup>
<h1>Heading One</h1>
<h2>Tagline</h2>
</hgroup>
And while I don't have a tagline per se, I have a short description about the company that totals up to 22 words. Should I put this in the h2, or should I drop the hgroup altogether and use put the description in a paragraphy? this is all going on in a < header> by the way.
Put the content in a paragraph. That's what paragraphs are for. The h2 should be a section's heading which is a concise summary of what the next content will be about.
<h2>About Company Name</h2>
<p>
This is twenty two words that describes our company. It is in a paragraph because it is content and not a heading.
</p>
<aside>Someone may post that this may appear as keyword stuffing to the search engines. I wouldn't worry about that. Twenty two words in a heading can happen naturally although it won't happen often. The worst thing that can happen is the keywords in the heading are diluted to the point of almost no value (or maybe even no value). So doing this for SEO purposes would not be beneficial.
If you're doing it for styling purposes that's not how HTML should be used. Use it for structure and CSS for styling. Not only does it make your site easier to style but it helps with SEO as semantic markup helps the search engines understand what your content is about.
</aside>
While there is probably no such thing as "too long," 22 words would be considered a very long heading.
Assuming you are doing this for style purposes, there is probably a better way to handle your tagline than with an H2 tag, which should be the second biggest and most most notable thing on your entire page. Stylistically, this isn't usually how taglines or slogans are displayed, even on websites. Just because it's in the header doesn't mean it's a heading. Think more like how a newspaper page is laid out. The H1 is the top, bold, big font, headline at the top of the front page. The H2 tag is the second lead story. The H3 tag is the sub-headline for that H1 story, and so on.
Assuming you are doing it for SEO purposes, then you are wasting your time. It is generally accepted that Google only crawls a certain number of characters in the title tags and header tags. If that is accurate, then all the words at the end of your your tag are going to be ignored anyway.
