We know for sure that domain names are very important for branding and business. But most of the people would expect http://www.example.com and http://example.com to be the same sites, right? But theoretically it’s not so. They are different even practically for some cases. But for most mere mortals like me, they will be same, and most people would want search engines to understand that. But some search engines consider them as two separate sites and as a result, the link juice, rank and crawling resources are split between them.
Here are my learnings so far from this -
1. Do use 301 permenent redirect as soon as possible on your site. The later you do it, the more traffic you lose. 
Here is how you can do it on Apache or IIS.
What is 301 permenent redirection?
2. Get into a habit of typing your URL the same way every time on web.
3. Google handles them well, because it has a preference setting in the Google Webmasters Tool. Even not using redirection doesn’t seem to cause any issues.
4. Live/MSN is the worst in this case, and it has several problems even with 301 redirects. See here and here. For them, you should probably use hard-coded URL’s, i.e. you should point to www pages even from non-www site (or vice versa), so that the link juice is correctly flowing to only one site. In Zamanzar’s case, as of now, I find several pages from both the sites indexed separately (www and non-www).
5. Guruji.com also has problems in this regard, and seem to index both kinds of pages separately. Not sure how much traffic they generate any way. 
6. Which one is better, www or non-www? Well, I would say the www version simply because of convention. Now, I myself haven’t followed this advice for this blog’s domain. Should do it now…
