I think a swing downwards is bound to happen, and soon of course.. however to call it a "bubble" is a little bit err, well, it's not the best wording one could use. It's a bubble once like 20x more people start buying into bitcoins, as in everybody you know. Right now it's just gaining some normal traction with a little bit of underlying pumps here and there.
by "bubble" I just mean temporary increase in value that is just floating in the air and ready to be popped by a major decision. This major decrease will obviously sway in bitcoins favor regardless as it is the most popular of most coins and the majority of new people who would like get involved and buy in think the price is too high right now. Also current investors will think this is a brilliant opportunity.