Just to give you an example, this is how my iPhone used to look (I had made a couple of improvements since this screenshot, but it gives you an idea of what can be done with Jailbreak.
With this setup, I had my dock icons transparent so you could see the clock, calendar and weather. There were also 2 'blank icons' for the spacing. I then recreated the dock above the calendar widget. Before 3.0 this worked perfectly since I did everything from the first screen (the top bar would load into categories - similar to folders).
With 3.0 and the search function, it slightly ruined things - plus everything ran slower for me!