How to eliminate certain words from tag cloud ?

I've looked at doing the same thing, and unfortunately Tagadelic doesn't seem to use any term-specific span or div IDs -- so the simple fix of "display:none;" in the CSS isn't an option.

What I'd suggest is creating a second vocabulary for those "non-topic" taxonomy terms. Then you can use the tag cloud block & page the include just your "Topics" vocabulary, as opposed to the entire-taxonomy ones.