Searching on the net there is a lot of talk about security, and that this is the better way to get involved. (downloading the original as it was meant to be, Bitcoin-Qt)
An online wallet is much easier and faster, but if one is thinking of getting involved with more than few hundred or few thousands USD, he/she would be somewhat apprehensive about the security issues, especially in view of all the hacking and funds disappearing from a great number of sites.
A recent example:
https://truthnewsinternational.wordpress.com/2013/12/03/the-heist-of-96000-bitcoins-us-103296000-or-e-76416000/
List of Bitcoin Heists - link from this forum:
https://bitcointalksearch.org/topic/list-of-major-bitcoin-heists-thefts-hacks-scams-and-losses-old-83794
Hopefully the next version will be solving some of these issues.
Right now, just to get the feet wet, few bucks and an online site might be the easiest way to start involvement.
Storing your bitcoins offline in cold storage is a good way to secure your bitcoins, using something like Armory:
https://bitcoinarmory.com/
There are new options coming out that will let you use a "hardware wallet" for keeping your coins easily accessible but preventing any form of hacking. One promising one that will be out soon is called the "Trezor":
https://en.bitcoin.it/wiki/Hardware_wallet