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I work for a company that closely mirrors the dropdowns employed by a very large ecommerce site - http://www.surlatable.com/.

Upon analysis of this URL, there are well over 100 links on that page because of the way their dropdowns are designed (over 400 in fact). However, upon close analysis, only 52 of these internal links are followed, and 370 internal links are not followed.

Based on this, I would recommend if you have well in excess of 150 or so links, use nofollow for those less important sub categories like this site has. (I'll have to change the structure of our site now...)

This is an interesting question. It also goes with what to do with a mega menu and all its links.  I've wondered whether the SE can understand that this is in fact a navigation (you would think they would) for internal links and not penalize your links in the body of the of the page.

According to Google's John Mueller when discussing about HTML5 he stated the following:

"In general, our crawlers are used to not being able to parse all HTML markup - be it from broken HTML, embedded XML content or from the new HTML5 tags. Our general strategy is to wait to see how content is marked up on the web in practice and to adapt to that ..." http://goo.gl/0YehV

You would then believe from that statement that the SE can differentiate navigation menus and drop down list from links in the body? I mean the SE must have crawled zillions of page and that would be a natural conclusion?

That being said I've use two strategies; the first embedding the select options in javascript... something like this

`**<script type="text/javascript">
/* ");
document.write("<option values=" ">Select a Property...<\/option>");
document.write("</option><optgroup label="Beach Estates">");</optgroup>**
document.write("<option value="\/alii-estate\/">Alii Estate<\/option>");** ......**

**......**</option>` 
**This seems to work well.... but not sure if it is actually crawled**

The other strategy that I am more in favor with is to position the  drop down list or navigation with a position:absolute; and
then place them physically at the bottom of the page ... this seems a better way, but it can affect the site links.

I've not done any real testing on this.

Burt Gordon 

Hi Guy. In terms of no-follow for page rank sculpting purposes, I've read the pros and cons of both and for me I've concluded I'd rather direct the juice where I want it to go rather than to block or prevent it from flowing where I don't want it to flow. No-follow can have unintended results, so I prefer the alternative.

Volume of categories and how to structure them is a challenge for a lot of ecommerce folks (me included). I've recently started flattening my site. While development of useful and intuitive sub-categories helps people find what they want on the 3rd or 4th click, crawl penetration suffers due to the depth. By flattening my site I mean reducing the number of sub-categories that can only be reached by other sub-categories - which is basically moving 3rd or 4th level categories up to the second level or top level (left nav).

A large and top ranking Toy Store I visit often to see how they structure their links has a top nav with categories, a left nav with categories and a sitemap in the footer. Each navigation entry has either different links in it or some different anchor text linking to the same pages. After much reading and apparent consensus among veteran users in this forum, I nixed the sitemap as unnecessary if I use good linking practice throughout the site. One Guru even suggested a sitemap can hurt your rankings if every page is linked to every other page with juice diminishing returns.

In my case, I created a left nav link to additional categories and put categories or sub-categories in them that were either: 1. Removed from the left nav because they were not important enough to be on the left nav 2. Removed from the left nav because on-page analytics suggested they didn't warrant being on the homepage. 3. Were a 3rd or 4th level category that on-page analytics showed there was enough demand to move its link to a second level or top level.

I hope this works for me and could of some help to you. Good luck.

10-15 dropdown links per tab is a lot to fit on the screen, but in my opinion the "too many links on the page" error is a bit overdone. How many total links appear on your pages on average? Unless you're blowing way past the general rule of thumb of 100 links, you're ok.

E.G. if most of your pages have 100-120 or less then don't worry about it. If most of your pages have upwards of 150+ links then definitely reassess how useful each link is to the user, and consider cutting down.

Here's an in-depth answer by Dr. Pete: http://www.seomoz.org/blog/how-many-links-is-too-many