WARNING: Most mod_rewrite rules do not work when previewing a site hosted on GoDaddy.com!
If you are testing out a website using GoDaddy's "Preview DNS" feature (e.g. http://domain.com.previewdns.com/), do not expect mod_rewrite rules in your .htaccess file to work. I could only get very basic catch-all rules to work. All other rules resulted in 404 errors.
After much frustration, a GoDaddy representative confirmed what I suspected:
"The mod_rewrite is able to function on the hosting plan. However, due to the dependency of the URL, for the rewrite to function, the Preview DNS may not allow it to function properly. If the rewrite is coded properly then it will function once the website is made fully live through our hosting plan."
So I guess the solution is to cross your fingers and hope that your rules are set up correctly.
I hope this saves someone else a headache.