I think what we know about Dashboard is that it is getting some enhancements to help people make widgets easily out of any web content that they access through Safari.
With respect to Spotlight, there have been some leaks concerning Leopard Spotlight's ability to do "operations" using some applications, sort of like Google. Like you can type a math formula in, such as ( 2 + 4.5 ) / 6.7 and you will get an answer from Spotlight, or you can type a word in and get a definitiion.
I think Leopard will be interesting next year, but I am in a dilemma because I *really* am wanting a notebook when Leopard and Vista are out, and yet I really want something smaller than the MacBook... Mmm, so my primary worry about Leopard is my geek lust.