A quick thought on when to use which
One of the discussion points that seems to always come up with SharePoint is when it is appropriate to use Windows SharePoint Services vs. SharePoint Portal Services.
While there are many good answers for this, I came across a nice little table in this article, on branding (a whole separate discussion), that I thought summarized it nicely:
| WSS |
SPS |
| Large number of sites with a small number of users for each |
Small number of portal sites with a large number of users for each |
| Team-based audience |
Organization-wide audience |
| Primarily for collaborating with other users on documents and creating lists |
Primarily for organizing, publishing, and summarizing |
| User-created and owned |
Created and owned by named portal administrators |
| Unstructured, created as a requirement is identified |
Planned and designed based on specific business requirements |
| Decentralized administration |
Centralized administration, with area delegation |
There is obviously more to it than this. I just thought it was a nice short explanation.