tedster - 2:04 pm on Sep 1, 2012 (gmt 0)
I changed my site structure from flat to hierarchical structure.
If you changed the URLs, it could be a long wait - I've seen it take 3 months for complete indexing in some cases. If you only changed the internal linking, registering the new link structure will happen a lot faster.
How many total pages are involved, before and after the change?