Google is probably the reason I was hesitant to use wikis. Google is very user friendly, and through our district Google mail, sites, documents, and calendars we can have more privacy, which is often important when collaborating with students. During the summer of 2008 when our district began Google mail, I began to "play" with Google using my personal gmail account. When school opened I was ready with websites and documents. It is now 2011 and I am still trying to have staff (administrators and teachers) buy into using Google anything; most are still stuck on Google mail, and even that is used ineffectively.
The biggest drawback for Google is using the discussion tool on Google sites, which is not user friendly. So, when Google groups was set up for our district in the summer of 2010 I was excited and established a few groups. Now we have to ask permission, and from my experience it takes too long. When all else fails, use the regular gmail, where there are no restrictions.
Collaboration via Google docs appears to be a great tool. I have attempted to use the tool with several groups, with little success. I think people are afraid, perhaps of losing information? I upload everything to do with my professional obligations to Google. I ask students, both adult and adolescent learners to use Google, but many resist. One problem I have encountered using Google within the district is that when I invite non district persons to collaborate, even with permission, it never seems to work. This is where wikis or personal Google would work better.
If I were to pick the winner for collaboration tools, I have a difficult choice. Google is simple and I have used it so frequently it is second nature. However, wikis are easier to access when outside the network, and the collaboration and discussion tools appear to be more utilitarian.