9/10 stop filters?

Looking at some of the photos people have taken using 9/10 stop filters has me wanting one for myself. Actually one thing I've always wanted to do was photograph the downtown during the day, but using slow enough exposures to blur out all the people.

For those who have them, how do you like them? Useful tool or gimmicky gadget?

I wouldn't call it gimmicky bcoz' it actually works. Do I like them? Hell yea'!