I am so greatful that you posted this Moshu. Because I use HostGator as well and my themes and images were not showing on the new wordpress 2.7 I am launching for a website. At first I thought it was an images permissions error and I was dreading have to change them because I have quite a few templates I am testing out.
Then I saw your reply that it was a Hotlink problem, so I check hotlinks and it was disabled already.
I ended up having to enable it, then disable it, last I added the direct link address to the hotlink list, enable it again and disabled it so that it stored the short form of the web address.
That did the trick.
So if you install WordPress 2.7 using Cpanel on HostGator.com, you'll need to go into your Cpanel, add the domain web address to the hot link protection list, enable it, and then disable it again if you want your hotlinks disabled, in order to get the themes thumbnails, and images to display on the front page.