If you're just getting started, I'd recommend the Beginner's Guide - http://www.seomoz.org/beginners-guide-to-seo

Also - You'll want to make sure you've 301 redirected all of your pre-existing .asp URLs to your new .php URLs. You'll lose all of your incoming links with the URL changes unless you are using an extensionless structure.

First - stay calm. Is your traffic noticeably dropping? Have you been penalized in any way in the SERPs? If not, you might just be experiencing regular fluctuations and have nothing to worry about. Look at that first.

Next, I'm assuming you have a Pro campaign set up.

The first course of action there would be to analyze your warnings, errors and notifications to minimize those. Fix the low-hanging fruit there and move on. Next, make sure you're following proper on-page SEO architecture throughout your site. Proper titles, H1s, interlinking, hierarchy, sitemapping, etc.

Now analyze your link profile. Do you have a lot of low quality links? If so, you may need to do some cleanup.

Additionally, you're in an e-commerce sector, so you may also want to check out the most recent Pro webinar - http://www.seomoz.org/webinars/ecommerce-seo-fix-and-avoid-common-issues

There are a number of things that can contribute to this. Without more information, all I can tell you is to start with the basics and move up. Have you made any significant changes lately?

Thanks guys. This is an interesting case indeed. Maybe it's just me being an SEO, but I tend to look at the URL on a good majority of the pages I hit. I don't want to confuse my users or provide them with inaccurate information.

.4mm and 4mm is a big difference.

I'm going to try out the decimal point and see how it behaves. I'll report back once we get the pages up.

I'm in the process of creating new product specific URLs for my company. Some of our products have decimals in them for their names as a unit of measurement.

For example - .The URL for a 050" widget would be something like:

http://www.example.com/product/category/.050-inch-widget

My question is - Can I use a decimal in the URL without ticking off the search engines, and/or causing any other unexpected effects?

Eeek. Sounds like one of those 5 signs that you've got a bad SEO client.

I'd be compelled to ask your client why he/she thinks this is a good business decision. Obviously the sheer quantity of followers you have isn't going to do a darn thing unless those followers are organic and relative to your business. It's just going to inflate his follower count artificially and add no value to the business.

I'd say the risks are worse than the rewards...

This is giving you a score of the popularity and trust of the links. Links that are more popular and that have more trust will provide you with better link juice than those with low popularity and low trust.

These pages should be helpful for you.

http://www.seomoz.org/learn-seo/mozrank

http://www.seomoz.org/learn-seo/moztrust