These days this is really like stock exchange - value is not backed by gold or anything, price is regulated by supply and demand. The amount of available BTCs increases by a rules set in stone, but other factors, like popularity, economy, Cyprus which all influence the exchange rates. Currently it is somewhat to gambling IMHO.
One basic rule is: if buying, only invest the amount you are comfortable with loosing.

Cheers,
   T

Theoretically the most secure way is running a bitcoind or bitcoin-qt locally, as you are in full control of both security and backup.
If you are unsure, run a closed source operating system or do not feel conficent in IT, this might be impractical though.

This is a good place to start: http://bitcoin.org/en/choose-your-wallet


Cheers,
   T

1 post needed to send PM, as written above.

Cheers,
   T