Negative keywords for the content network?

Will doing this block sites I want?

[limitup]

Say for example I have a keyword-targeted content network campaign promoting widgets. Today I notice a sewing site displaying my ad, and I don't want my ad on this seweing site so I add the site to my exclusion list.

My next thought is to add the word "sewing" as a negative keyword, but I'm curious if anyone knows exactly how the negative keyword matching/blocking works.

If I add sewing as a negative keyword, and a great widget sites happens to mention the word sewing somewhere on the page/site, does this mean my ad won't show there either?

I guess what I'm wondering is how simple or advanced is Google's negative matching system. Does it just look at the negative keywords and not show your ad on any site that even mentions one of these words, or is it somehow smart enough to know that a great widget site that happens to mention sewing in an article, etc. should still show my ad?

[buckworks]

If a page mentions "sewing" your ad won't show on that page, but it won't be blocked from other pages on that site just because a negative keyword is mentioned on one page.