I recently received the following email and thought it would be good to share my answer.
To your knowledge is it acceptable to drop the use of www. before your web site?
This is not only acceptable, there are some people who feel that it's valuable to stop doing it in general.
However, the answer really depends on the context of the question.
Using www. in Email Clients
Send an email to yourself with the following text:
1) example.com
2) www.example.com
3) http://www.example.com
4) http://example.com
For me, the third and fourth are automatically formatted as clickable links but the first and second are not. So, the third and fourth are more likely to be noticed and clicked on by users of email software like mine. This is, of course, dependent on how and where people read their emails and varies wildly.
Also, as your eye scans through a body of text the second one is easier to recognize than the first one. However, some people feel that for emails the third format is disruptively long.
WWW or not For Search Engines
Another consideration has to do with search engine performance. If you have some links to your site that point to both versions this can confuse the search engines about your site. Most search engines have figured this out or provide tools to tell them which one is the "right" one, but it's best not to have the problem at all. You can use a "301 redirect" to forward the users (and search engines) to your preferred version and prevent the problem in the first place. If you are unsure how to do this, your website developer should be able to help you.
Final Decision on WWW or not?
