After a brief round of non-code related posts, I am back with one for the developers in the audience... literally. At my event in Bloomington, IN today, one of my MSDN Events attendees ("Visualize the 20" - a brief inside joke specifically for his benefit) observed something special during my InfoPath with SP1 session (viewable as an on-demand webcast) - when I changed the data source of the InfoPath form to a new schema, little lock icons appeared next to the fields in the Data Source task pane. I had never noticed it before, so I promised to research this phenomenon and post it to my blog.
Well, I have an answer. There are lots of unique and informative icons integrated into the design environment of InfoPath and you can find out all about them with this brief write-up "Understanding key design mode icons". If you want to dive deeper, check out Thom Robbin's blog post entitled Introducing XSD - his post gets more technical about *why* InfoPath "locks" the fields.