I made a macro to fill the gap between uniform and gaussian blur: Hybrid Blur
You can get it on my website: [size=12pt]http://nkblog.nkdev.de/?page_id=446[/size] it’s at the bottom of the page.
It’s supposed to be faster than gaussian blur but without the artifacts uniform blur creates. Here is a comparison of the two existing types of blur and my macro:
The results are better than I thought and it’s 35% faster than gaussian blur!
That’s probably not a relevant speed-up for small terrains built on fast multi-core machines, but in certain cases (large terrains, lot’s of blurring, slow machine) it can save you some time.
Having used a 650MHz pc myself, I know that blurring can in fact take long enough to wish you had a faster blur device 
edit: btw this implements filtering with the triangle function. (As opposed to gaussian and uniform blur which use the gaussian and rectangle function respectively)