Spiders from search engiines "crawl" the web by following a link from one page to another.  Using a rel=nofollow HTML attribute on a link tells the search engine not to follw the link and crawl the page that the link points to.

Search engine rankings by sites like Google are based on the premise that the best content has the most links to it (this is a super over-simplification, I know).   "nofollow" links aren't counted by Google when they assign value to the page being linked to.

Most often sites use "nofollow" to block links from user generated content that might be used to manipulate search engines.  An example of this might be a blog that nofollows all the links in it's comments so that spammers don't show up and flood the comment section with links to sites they'd like to rank higher in google.

If you are happy with any URLs with query strings not being indexed your robots.txt will work fine.

Do any or your URLs with question marks in them have links to them?  If so you might want to be careful blocking google from indexing them.  I would think you'd lose the benefits those links would pass to your site.

I don't know if there's a good solution with robots.txt given your URL structure.  However, you could use the rel=canonical link tag in the header to force google to treat many of your URLs the same way.  This would help you avoid duplicate content penalties.

More on rel=canonical:

http://www.google.com/support/webmasters/bin/answer.py?answer=139394

http://www.seomoz.org/blog/canonical-url-tag-the-most-important-advancement-in-seo-practices-since-sitemaps

Personally, I would avoid this strategy.  If the site selling the dofollow comments is caught by Google then Google could determine that you bought a link and penalize you.

Can you find any sites in your industry that remove the nofollow tag from comment of users who participate a lot on their blog?  I'd focus my efforts on such sites.

Not that I'd necessarily  recommend this, but you could always report your competitors to Google if they are indeed buying links.  Before you do this I'd make sure that you were playing by Google's SEO rules.

Hey Domaon,

This happened to me once and I was furious.  I would contact the publisher and show them this article.

http://www.mattcutts.com/blog/pagerank-sculpting/

Basically it explains that the site gains no additional PR to it's other links by  nofollowing your links.   Who knows maybe they'll chance their stance on nofollowing links to use submitted articles.

That said there are good reasons why a link can have a nofollow attached to it.  However, if you contributed an article to an ezine that selectively publishes user submitted content you deserve a "dofollow" link.

You don't have to create anything to start planning out your URL structure.  Lots of times when building something I think about the keywords and then just start laying out the URLs that I think will suport those keywords from a search and overall usability perspective.  I'll do this even before I start mocking things up.

From your design you could put all mowers by one company on the same page and then have tabs to separate the content.  Implement the tabs in javascript so that they just enhance some good solid HTML lists or divs.   That would create one page for each mower brand.  Are you hoping to SEO well for "mowers" or "toro mowers"?  Perhaps you are already planning on doing this?

In regards to the anchor text, can you just link to "Toro Mowers" and then have people click the tab they want.  Othewise perhaps you could do something link "Toro Mowers - Home",  "Toro Mowers - Commercial".  At least that gets the keywords at the front of the anchor text.

The structure of your site will be important for SEO but start by finding the list of keywords to target.  Consider keyword competition and search volume when making the list.  Come up with one page for each of those keywords. Then try to come up with an overall URL structure where you can SEO all those pages well.  Finally, don't worry about SEO on each and every page you create.  You are going to have some pages that add to the overall experience of your site that might not target keywords.

You are smart to think about creating only the pages that you have good content for.  I wouldn't force myself to create any other pages.

Could you be more specific?  I'd love to see the full URL path before of the categories and sub categories before I weigh in.