I wanted to use nested expand shortcodes and found that wordpress doesn't support that out of the box.
I have modified collapse-o-matic.php so that it supports nested expand blocks. The code comes originally from the way the j-shortcodes plugin handles it (you can see this here: http://plugins.trac.wordpress.org/browser/j-shortcodes/trunk/j-utils.php).
Here is my modified collapse-o-matic.php: http://pastebin.com/kNRiRG2P
I thought I'd post this here in case the developer wants to include that in the plugin or anyone else wants to use it.
[expand title='Root Expand block'] This is the root expand block. [=expand title='Nest level 1'] Nested block level 1 [==expand title='Nest level 2'] Nested block level 2. [==/expand] [=/expand] [/expand]