I have found here on AU and elsewhere that Shotwell can import files and organise them into folders/subfolders by date (yyyymm, yyyy/mm/dd, and so on).
Can I import files, assign them to events, and have them organised into folders by event? Something like Pictures/Event A, Pictures/Event B, or (even better) Pictures/201111/Event A, Pictures/201111/Event B, Pictures/201112/Event C.
Not yet. Shotwell can organize your photos into folders by time only, like the first link you have. To achieve what you want you need to use the Hierarchical Tags feature in Shotwell. This isn't exactly what you want though, so the short answer is no.
Have a look in Preferences/Library/Importing/Pattern: and click (Help) for a list of exactly the time-based metadata Shotwell can organize by.
If you are just wanting to separate out groups of photos to export, you can select a group of tagged photos and export them to a new folder. From there, you could manually reorganize your Pictures directory structure in the file browser.
