I left Dashboard enabled, because with all the widgets closed it doesn't actually use any RAM. Only if you have widgets open does it really matter.

However, I did disable Spotlight and notice a massive difference, using the following commands in Terminal:

DISABLE & ENABLE SPOTLIGHT
To switch it off:

sudo mdutil -i off / /Volumes/*

To remove existing indexes:

sudo mdutil -E / /Volumes/*

To switch it on:

sudo mdutil -i on / /Volumes/*

Click to expand...

Switch it off and remove the existing indexes to disable it. The third command is only if you ever wish to switch it back on again. You will still be able to use Spotlight, but it will do a classic/manual search rather than scan the index.