If I had 0.00001 bitcoin for every time I have heard bitcoin is in a bubble I wouldn't need to be on Steemit. Well, since Steemit is such a cool platform I'd probably use it anyway even if there were no rewards here.
Charles Hugh Smith recently posted a great article on his blog discussing the possibility of bitcoin being in a bubble and it is a really good read. I don't like to plagiarise other peoples work so please check it out if you're interested.
The chart above should be self explanatory. :)