"Speculative" is the right word.
It's extremely volatile and unregulated. I'd tread very lightly with it. And I'd rather wait until it sells off hard again - I'd rather buy 5 shares at $500 the next time it sells off than pay $2500 or so for one share today.
This is the kind of thing IMO that people generally shouldn't fool with at all until they've got at least 6 figures worth of assets - at least those who want to manage risk and are serious about keeping their $ and growing it into a large nestegg over the long haul.
If you've got $100k for instance, most inclined to speculate in bitcoin would probably be better off with $5k or less in bitcoin... buy it when it's sold off hard, then sell some or most of it when or if it roars back up again in the future.
At least $5k in cash...
Maybe $5k in a good, solid gold ETF (that buys the physical commodity and uses little leverage)...
Perhaps another $5k in another alt investment such as a REIT or something that shorts the broad market such as
http://www.morningstar.com/etfs/ARCX/SH/quote.html
The remaining 80% or so could be split up more or less equally among 15-20 or more stocks spread out pretty evenly among the 11 main sectors of the market - buying 15 or more largely uncorrelated assets will greatly reduce portfolio risk during bad times.
If you only have a few thousand dollars, I don't think it's a good idea to put all or most of it into a share or 2 of bitcoin while it's heavily overbought and sitting at or near all time highs. I'd build up a solid foundation of assets before doing any speculating. But that's just me.