Dashboard isn't "the killer app", but that's not to say it isn't useful. I have found it to be a time saver (at the expense of resources) in a few tasks. Allow me to illustrate.

Home

In the morning I drag myself out of bed and attempt to feed myself. I'm sure it's a comical event, one which my children will laugh at many times. During this entertainment extravaganza I usually check a few things on my trusty iBook: the day's comics, some blogs, and Dashboard. Dashboard will tell me in a glance if I need to dress warm or cold, expect rain, snow, sleet, or sun, and give me an idea of the wicked pollen and it's continual struggle to kill me. If I've purchased something online I'll usually also track it on Dashboard, so I'll know, "Hey! Why did my package go from Nevada to Kentucky?!?"

Work

My office doesn't afford me a view of the outside. It's terrible in that respect. I never know how the weather is doing, and in the cold months of the year (or April) I like to keep an eye on the freezing point so I can make a hasty exit and work from home. That and it's always fun to comment on the weather in chat, because inanity is great stuff! Beyond this I find that I need to generate random passwords for db connections, random text for site layout testing, and sometimes need to know the HTML entity for something strange like the Yen (¥ btw).

For whatever reason people are always asking me about dates. And I hate loading up iCal just to refer to a date on a calendar, so I just go to Dashboard and look. Takes me a brief moment. I also drop sticky notes on my Dashboard from time-to-time, which keeps things greatly uncluttered.

In summary I use Dashboard for those things I only occasionally need, want to keep hidden but resident, and for those things where a quick glance at data is all I need to answer my question. A push of F12 and I get my data is fast, easy, and most of the time I don't notice the missing resources.