Views Optimized provides an API to seperate filters and fields to optimize certain views.
The process does not yet work fully automatically, but with some knowledge of the view _huge_ savings can be made.
1.2 s -> 0.14 s (0.07s for the query and the count_query).
The idea is really simple:
Separate fields and filters and conditions.
You can read more about this here:
And now have fun! An example for events is in the README.txt.
*Note:* For Developers only for now! This is an advanced module and you'll only need it to tweak the last bits of speed out of your views, after index optimization, etc.
*Note 2* Views Optimized is only available for D6 and has not been tested with views 3.x, yet.