Yes and no. First of all, at least until recently, a hashtag wasn't actually distinguishable from the word itself. So 'ycombinator' and '#ycombinator' would bot

Yes and no. First of all, at least until recently, a hashtag wasn't actually distinguishable from the word itself. So 'ycombinator' and '#ycombinator' would both show up in a search for 'ycombinator' (and that was intentional. If anything, they were making it easier for people to ignore them (if they wanted to). Second, the hashtags (as well as the @replies) both grew organically out of the userbase. They adopted them because the users had already adopted the hashtags. In fact, if I remember correctly, they were initially resistant to the idea until they saw how much people took to them and used them even without any official support. The new tab seems like a glorified search - they use a hashtag for an icon, but it seems like the system itself would work pretty well for any single-word search. And with a data firehose as fast as Twitter's, you don't really want to have to do search over multiple words if you can avoid it.