Dashboard is what you make of it.
If you load it up with shit, ya, it's going to suck. The default widgets are to give people and idea of the range of things that are available and all have some use the OS itself isn't already supplying (i.e., the "clock" isn't just an echo of the time in your menubar, it can be the time of ANY time zone...which is extremelt useful for some people).
There are some extremely cool uses for dashboard and, if you have enough RAM, its presence is welcome.
The widgets I use provide me with quick access to the following:
Weather Forecast
Radar
Sticky Notes
Yellowpages
Gas Prices
Who's accessing my webserver (via a shell-command widget)
Being that I use each at least once a day, it is well worth my spare resources (I have 2GB RAM). If these aren't useful, or you run with a lower amount of RAM, you may want to use fewer widgets, or disable Dashboard all together.
Oh, and widgets are "software" just like any other app your run. If your Dashboard is unstable or slow, make sure it's not the fault of a particular widget managing resources incorrectly.