Didn't have as much time today, but here are my findings:
1. A standalone ProcessBook installation requires a huge dependency package. So if you intend on deploying this on hundreds of PCs, better think of it. It should be installed on a TS, or deported using Citrix. Of course, for large scale deployments, it is better to plan using Web Parts over ProcessBook...
2. PI Datalink 2010 is supported on Excel 2010 32-bit only. It's documented in the Release Notes but as usual I didn't RTFM, and had a 64-bit installation. The PI-DL installer doesn't tell you anything about this, and it results in the add-in not being installed in Excel as it should be.
3. If SharePoint was a blind date, I think I would stay polite, possibly pay the whole bill, then say goodbye with a kiss on the cheek... i.e. leaving all options open while sending a clear message at once. Web page editing is sluggish, which is unacceptable in 2011 for a web application and I don't care how slow the back-end is. And it is hungry as hell. Even a vanilla installation revealed a lot of clunkiness with some "oops" error messages and dead links. Bottom line is I don't like SharePoint as of now, but I'll have to get used to it.
4. The drawing on my first post isn't right. I'll need to fix it in an update.