This is caused by browser caching and/or the mechanism we use to efficiently distribute your content within our network. If you wait a few minutes, the files should resynchronize automatically.
If you prefer not to wait, you can also help the process along by visiting the modified page yourself and doing a forced reload. For Internet Explorer and Chrome (Windows), this is done with CTRL-Refresh (or CTRL-F5) and with Firefox, Safari and Chrome (OS X) this is Shift-Reload (Ctrl-Shift-R on Windows, Command-Shift-R on Mac). This will force that page and all related content (images, .js files) to be resynchronized immediately. Since we have a lot of caches and requests are load balanced among them, you may need to do this a few times to get every cache that might answer for your site.
If you wish to do this from the command line, you can use curl to force the refresh:
YourPrompt> curl -H 'Cache-Control: no-cache' -i http://www.example.com/stale/content/url
Again, do this several times for each affected URL to make sure you get all the caches.
There is a case where if you access the site before the IP addresses are assigned (within the first minute after it's created), you'll get a DNS error. Once that happens, some versions of Internet Explorer will keep returning errors long after the site is created, even if you use a forced refresh. Waiting a few minutes, restarting IE, and sometimes rebooting have all appeared to help this under various circumstances.
If your site is correctly set up but you have not uploaded any content, you should see a "Not Available" message when you access the site, which you should be able to "refresh away" once you have uploaded something.