Ever want to change your permalinks category base from 'category' to, say, 'in' ?
Just enter 'in' (without the quotes) in your permalinks category options page.
But .. you still need to rewrite your urls for search engines and visitors with bookmarks to they land on site.ext/category/newyork to site.ext/in/newyork
Just enter this in your .htaccess file and you're done!
RewriteRule ^category/(.*)$ in/$1 [R=301,L]
Ending with a special thanks to Tom Dullemond: http://www.seoservices.nu/