Nice work!
A few suggestions which come into my mind:
Would it be hard to implement a method which replaces the #hash words with actual links to the tag? It seems a bit weird to have #some words in a #post look like this without actually doing something.
Also: Maybe it would be a good idea to add an escape mechanism to the system. Lets say, all #hash tags which have a \ before like \#this don't count as tags. For example in a coding forum:
Code:
#include <stdio.h>
morecode
Would create the hashtag #include where it probably shouldn't.