That's a good question. Due to the design of bitcoin, it is a bit difficult to "loan" them (remember that banking is effectively a loan where the bank pays you interest).
Now, that's more on the theoretical side of things. In practice, a major problem with loans in Bitcoin are the volatile price. If the price rises suddenly, it could become more difficult to pay back interest; or alternatively if the price takes a heavy drop, the investor may lose money as what he is paid is less valuable now than it was at initial investment.
why is it difficult? it is the same as lending money. when someone files for a loan, bank reviews their application takes a collateral and gives the loan and then takes it back on intervals. Now, that's more on the theoretical side of things. In practice, a major problem with loans in Bitcoin are the volatile price. If the price rises suddenly, it could become more difficult to pay back interest; or alternatively if the price takes a heavy drop, the investor may lose money as what he is paid is less valuable now than it was at initial investment.
and price is no matter, because they lend bitcoin and receive bitcoin. and this can only happen in the future when mass adoption happened and price is already high and stable.
it is like lending USD and then USD price going down versus another currency!! that has no effect on how lending goes.
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Bitcoins are not fiat, and therefore, can not be continuously printed. Because of this, no one can guarantee to indefinitely keep paying out interest on loaned coins. A horribly exaggerated example, just to make a point, is that if I somehow had 20,000,000 bitcoins in a bank, they could never pay me more than 1,000,000 total in interest just because of the limited supply.
bad example. if someone has 20 mil coins it means bitcoin is dead since 1 person controls all the supply and nobody takes a loan 
Good points, BTCLovingDude. I'm not sure I follow what you mean with regards to the USD price being less than another currency. If you loan USD and are getting paid back in USD, I'm afraid I can't see where the "other currency" comes into play. In my example, I meant a "pure" bitcoin loan where you loan X bitcoins and get Y coins back at regular intervals in interest, without translating to another currency.
As for part 2, guilty as charged. That is a bad example indeed. It was hyperbole to make my point. If there are only 21 million bitcoins in existece, and we're not continually printing them up, we can't guarantee interest back on investments indefinitely. Of course, short term investments should work just fine.
It's a good idea. Must work hard in able to save bitcoins. Bitcoins is such a beautiful idea kind of new currency. With bitcoin it has many advantages. If you start saving now in the future the value of it will be raise and if you already have many in the future you will be a millionaire. And it's because of your hardwork and patience. You'll be able to sustain you everyday need and probably in the future you'll able to buy all the things that you want. But remember if you saving bitcoin, don't forget to make a bussiness or investing it so that even if your using it still it earns and double. Goodluck to all who wish to save bitcoins.
