Actually, it's not so much that the Wikipedia blackout is easily circumvented as that it can take effort to see it. To see the blackout required allowing 3 ( maybe 4 ) domains to provide javascript. No javascript gives a message about the blackout and about SOPA/PIPA and the normal english site full of functional articles and links.
The blackout probably still hits the target audience because they won't know they should turn off javascript, but it's a shame it doesn't work. FSF, BoingBoing, 2600 and Google all demonstrated the blackout without requiring javascript. EFF and CreativeCommons, like many others, has a prominent article about the blackout, but the site is still intact.
Anyway, happy blackout day to you :).
Update: On the other hand, the Wikipedia blackout is the top story in the BBC hourly news right now.