Massive drop in all ranks after preferred domain changed in WMT

A few days ago I changed my preferred domain in WMT from "Don't set a preferred domain" to the www version. I just wanted to be sure all my backlinks where being picked up (from the non www version of my address).

An hour after i'd done this my main keyword dropped 20 places.

The next day all my keywords had dropped.

Today some are ranking in around 80th but for the wrong pages. So the keyword "blue widgets" is showing my page on "dark blue widgets".

Has anyone had this happen to them? I'm pretty confused as to why this would happen :s Do I just need to wait it out?

I don't think it was to do with the new panda update, my site danced a little from that but nothing like this.

One hour sounds a too short time for any webmaster changes to take effect.
Mostly,it was a coincidence.

It could have been more than an hour, 1-3 hours, I cant remember exactly. But yeah that does sound a little bit too short. Im hoping it's not a unnatural links penalty for which I've just not received the WMT message yet...

Really annoying, my first site which has had any real success.

Not sure what made you set the preferred domain name.. changing such things (including website template, etc) can affect your SERP's. However, few hours is too little a time frame. Give yourself at least a week or two. In the mean time make sure your domain redirects properly, with and without www.

I just wanted to be nice and clear which version of my domain I wanted to be my primary. But yeah, I won't be doing this again in the future haha. Didn't know it would cause this to happen. I redirected the non www to www earlier today.

Don't understand why you did this if you wanted to make sure all your back links were picked up? Surely choosing between one or the other would lessen the amount of links?

You could use rel canonical tags in the header to tell Google which version of your url links should point to.

Yeah Jimmyn, think i've made a pretty big mistake

Misunderstood what it did

Think I should change it back?

I'd try the rel canonical thing if you don't use it already. It's supposed to direct all your links to one URL.

http://googlewebmastercentral.blogspot.co.uk/2009/02/specify-your-canonical.html

If you're using Wordpress, i think some of the plugins offer the function. All in One SEO i think does.

Meh ill wait it out. Read this on webmaster tools help

"we'll take your preference into account when displaying the URLs. If you don't specify a preferred domain, we may treat the www and non-www versions of the domain as separate references to separate pages."

Just wanted to avoid that really.