Cryptocurrency Mining?

Something I've been seeing a lot lately. I looked it up and I now understand a little about it.

Mining seems to be related solely to Timestamping. Since this seems to be a CPU intensive thing to do, it is outsourced and hackers are paid for doing it for the company providing the currency. They're getting paid in that companies own currency, right? But why does it need to be running all the time? How can it be so damn resource intensive? From what I hear, the payment doesn't even cover the cost of electricity used to do that. So cryptocurrency mining is only attractive to those who don't pay their own bills ("mom's basement")?

A few more questions about cryptocurrencies in general, to those more versed in it than I am:

• How can it be of any use if there's more than a thousand currencies? How can I use any currency outside of its own scope? are they interchangeable? simply put, what do i get it for (besides mining), and what can i get for it?

• I understand it's decentralised. I understand that this is possible and makes sense, but then again, how can there be thousands of currencies? there seems to be a contradiction there somewhere. Also I'm reading about cases where one server shut down and people lost all their "money". So how's that possible.

• There seems to be an incentive to create new currencies or servcies around existing ones. if it's decentralized, what is that incentive, besides getting a few adclicks?

• Who is actually paying bitcoin miners, if it's decentralised? Who is organising the flow of services rendered and payment?

• Why is it so damn popular? Is it really just a bubble?