Google Wave vs Sharepoint
Solution 1:
Google Wave is cool - but it's, at best, in a pre-Beta stage. With SharePoint, you get a stable (relatively) product - with a clearcut path and mission statement. The Wave may be the next big thing - but it's not here yet.
Solution 2:
While I am a huge Google fanboi, the biggest downside that I see to using Google Wave is that its not just in an 'eternal' beta phase, its very young technology. Google is still tweaking the API. Couple that with the fact that Google is still pretty new to the corporate applications arena and you're setting yourself up for likely disappointments and failures early on. Given a couple of years, this will probably be a superior solution but I for one am not convinced that its ready for prime time.
On the other hand, Sharepoint is a much older, more established application with a proven track record and a solid code base. Of course this fact tends to be a double-edged sword because that means that it also suffers from design decisions and coding practices that could now be called archaic.
I suppose a large question for you then is whether stability and reliability are more important in your choice of collaboration tool, or if you'd rather go with a tool that is likely to pioneer the next generation of online collaboration and suffer the bumps that will surely accompany your journey.
Solution 3:
If you work for a publicly traded company and you're collaborating on anything even remotely secure (network setups, firewalls, passwords), then your company's legal team and compliance team will probably have fits if you put that data in Google Wave, a cloud-hosted service. SharePoint still has security risks, but at least the data is hosted internally, which won't elicit as many screams from the compliance department.
If you ever plan to cooperate with other company departments (Windows, SQL, application management) they may not be as quick to adopt Wave either.
Solution 4:
Primary collaboration tool to do what? I can't help thinking that both of them enable slightly different kinds of teamwork.
I'd also suggest that sharepoint might be expensive and complex for a departmental internal tool, but is the choice really one or the other with no alternatives.