Another thing I noticed, is that the buttons are bad compared to the 504, they are small the the symbols are painted on, so the markings may eventually fade away, but I guess compensates with an amazing touch screen. The dedicated volume up/down button is a plus, however I hate the new location of the OK/Cancel button, it's way at the top, and it'll take a long time for me to get used to.
Buying the plug-ins was instantaneous, unlike with my 504 which took about 8 hours, but I guess it's an improvement to the Archos web store not the 605.
I don't see a resume button on the home screen, which is a bit disappointing because it's a very useful icon that was there on the 4th generation. Correct me if I'm wrong, I hope I'm wrong and haven't found it. I know they removed it because the 605 has so many features that it is impossible to have icons for every single thing. Which brings me to my firmware update suggestion to have the option to customize the home screen to individual needs. I personally would get rid of Widgets from my home screen and put a Resume icon instead.
I didn't expect the web browser to be this good, it's really spectacular (for a mobile device) it renders web pages very well to fit the small screen, and it's great for basic web browsing. But it tends to slow down on sites like digg, where there a lot of code to process. But it's not at all bad because many of these resource intensive sites like digg and engadget have mobile version that are very lightweight and are designed to work on phones, there is even a mobile version of google maps that works completly lag free on the 605.
Edit: The speaker is also a lot louder on the 605 then on the 504, and I also think the volume out put to the headphones is a little bit louder then the 504 from what I can tell.