A lot of ecommerce sites these days are implementing dropdown menus for the main navigation.  Ecommerce store owners need to be careful with this, as this could potentially reduce your competitiveness on the search engines.  Let me explain:

  1. There are many way to program dropdowns and most of them are not “search engine friendly”.  This means that if the main navigation of your site is not usable by the search engine spiders (that come regularly and index all of your pages), that means that many pages on your website will no longer be accessible (other than direct access to the URL) by the spiders.
  2.  The potential impact of #1 is that the internal linking architecture of your site is massive when it comes to competitiveness on the search engines.  Making sure your main navigation is usable by the spiders and that your navigation also takes you deep into your subcategories can help you compete better.

So, be careful with dropdowns.  If you have to do it, I would suggest using DHTML (not Flash) and supplement with another navigation of your categories/subcategories elsewhere on your site template (that’s accessible on each page).