With the hi-res screen, you are able to see 4 times as much and colors are more vibrant and brighter in general. Holding the two models side by side is night and day, basically.
The web browser (Blazer) loaded on the 600 is an older version from the 650 version I believe. I know that the controls are at the top instead of the bottom and it seems to support different web standards. At work, I have yet to have enough time with the 600 to pinpoint what those are, but we're having significant problems with the 600 in my web application development that we aren't seeing with the 650.
Sprint sold me my 650 for the full grip, but thats the pain of being halfway through your contract.
