wikis are very effective
but....
you gotta be careful about it.
1st. there are a LOT of wikis you do not want to hit
if, say, the wiki for semantic indexing got a page about your site put on it, well....you just told google's data analysis arm that you are spamming and gave them a copy of the footprint.
or if you spammed the wiki of a community that google employees are members of, you probably just are asking for trouble.
it's been said before that some wikis seem to be able to signal directly to google
and i know that those two wikis are not the only honeypots out there.
i just know i saw those two wikis in the big list that was shared here earlier.
i refuse to purchase wiki services from people because of this
after all, if you buy wiki services, you'll go with the one providing the most links
not the one that has the most filtered and safe list.
and it's not their site, so what do they care?
i use wikis, i go wikijacking, make sure the wiki is over 1 month old, with no recent edits, and is targeted at the niche i'm targeting
then i replace it's links with links to article submission livelink results
add it to a list
comment blast the list at the end of the day, then ping the crap out of it with about 3k pings / site
works amazingly