Why do many sites using "#!/" for AJAX?

Question

Possible Duplicate:
What's the shebang/hashbang (#!) in Facebook and new Twitter URLs for?

Many Ajax sites use #!/ in their URLs. Examples include Twitter (https://twitter.com/#!/Linksku) and Grooveshark (http://grooveshark.com/#!/).

Why do they use the exclamation mark?

Answer 1

https://stackoverflow.com/a/4175129/1232478 links to two Google items that explain it pretty well. In short, it helps make AJAX sites crawlable.

http://googlewebmastercentral.blogspot.com/2009/10/proposal-for-making-ajax-crawlable.html

is ultimately the link.