I agree that out of the box, the AppleTV is limited as to what it can do. However, spend $49 on ATVFlash www.atvflash.com and you can attach an external USB drive for storage, run Boxee or XBMC, use a web browser, and play ALL the media that is on your Mac. Check the website for all the other features that ATVFlash adds.
I know that people will say that ATV USB Creator is free http://code.google.com/p/atvusb-creator/ but it is limited in what it can do and mainly offers Boxee/XBMC. It allows you to SSH into the ATV but everything else has to be done by hand. ATVFlash automates everything for you. Thereofre it is worth the charge for me.
I totally agree, I have installed atvFlash and feel its well worth it. I know that there are other sites that have the free version of this type of program but that works only if you are savvy about installing. I liked that someone had done all the hard work and packaged it into a newbie user friendly program. Now my AppleTV is so much better. In fact I am using it and the Firefox app that is now installed in the Apple TV and using the wireless keyboard and mouse that is attached via the usb hub to the it as well to write this. If and when a new updated version of Apple TV comes out with all these features then I will purchase it and put in in my main home theater and move this hacked one up to the bedroom system.