Just a comment regarding the Konfabulator vs. Dashboard comments below.
First, I have to say that Dashboard was a big disappointment for me. Maybe it will become a great addition to any system in the future, but as it is now, it is far from being great. The main issues that made it unusable for me are:
1. Widgets do not coexist on the Desktop. To use Dashboard you have to switch in and out of it. I prefer Konfabulator in this sense.
2. Some Widgets (e.g., Weather) will not remember their preferences/settings once they're closed. Again, I prefer Konfabulator.
3. Each open Widget uses 20-30 MB of memory even while they are on the background. I have no preference here, since widgets for both programs use a similar amount of resources.
In terms of having useful widgets, I found quite a few of Konfabulator's widgets to be useful. In many cases I prefer to use regular applications instead, though, since they are less taxing to my system. For example, You Control (which can and should be improved) can substitute at least 6 widgets for me, including Weather, iTunes control, Pasteboard, System Monitor, RSS feeds, and Date/Time/Calendar. All these features are available using less resources than Konfabulator (or Dashboard).
Regarding the comment that Dashboard costs no more, I'm not sure that I agree. While it is included with Tiger, Tiger was not a free upgrade (Microsoft users may be getting more free upgrades than Mac users ;-) ). There may be additional costs that are not evident now. One that comes to mind is the potential cost in the development of Mac software. Will developers have any incentive to keep on making great programs for the Mac? After all, there are many similarities between Dashboard and Konfabulator. And let's not forget Watson (RIP) and Sherlock. And how many Mac users are using an MP3 player that is not iTunes? Audion was great, Unsanity Echo was promising, but they are no more :-( Can something similar happen with web browsers? What about email programs? There are certainly many potential costs worth considering.
By the way, I do believe that Tiger is a worthy update to OS X, but not because of Dashboard (or Spotlight). In addition, while I prefer Konfabulator over Dashboard, neither one is for me. Fortunately people can download Konfabulator, give it a try, and then decide. :-)