I'm happy to see that Google has gone with a clear, direct anti-SOPA message: "Millions of Americans oppose SOPA and PIPA because these bills would censor the Internet and slow economic growth in the U.S."
And their call-to-action message on the home screen: "Tell Congress: Please don't censor the web!"
Simple and clear.
Wikipedia's message is much more vague and indirect: "Imagine a World Without Free Knowledge ... Right now, the U.S. Congress is considering legislation that could fatally damage the free and open internet." [How?]
And then their detail page (http://en.wikipedia.org/wiki/Wikipedia:SOPA_initiative/Learn...) spends the first three bullet points talking about details about the Wikipedia action (how long they will be blacked out for, how they decided, etc.) before getting to: "SOPA and PIPA are real threats to the free and open Internet." Okay you've got my attention. Go on... "Although recent media reports have suggested that the bills are losing support, they are not dead." Argh! If I haven't been following this debate, why do I care about the current health of the bill? Tell me what's going on and why it's important!
This reminds me of their recent banners soliciting donations, which other commentators have pointed out were indirect and not as effective as they could have been.