Exchanges being hacked, Exchanges stealing money, Wallet services getting hacked, Your wallet getting Hacked or deleted, Misplaced, stolen, or forgotten private key
Security is generally increasing, Rome wasn't built in a day. Just see how long it's taken for something like MS Windows to become reasonably secure. Sites will improve their game with increased competition, and better tools/software for personal wallet management is inevitable as the user base grows.
Unless you use escrow (which involves trusting a third party) the buyer risks a no delivery of goods and/or services with no recourse. Check out the scammer accusation subforum.
No chargebacks is an inherent feature of bitcoin. It doesn't really increase risk though, it just MOVES risk from the receiver to the sender. The flip side is that it's much safer to GET money with bitcoin. In any case I suspect escrow services will become standardized with time.
You also have to download a bloated blockchain (which takes forever, hogs space on your computer, and may contain child porn) or trust a third party wallet source
Full blockchain download isn't required for everyday use, use eg. MultiBit. In any case this is a software/optimization issue, as there are many suggestions for how to improve performance even for full clients.
As far as I can tell, the miners and devolpers are the government. When the blockchain forked a month or two ago, the developers and miners (or at least a mojority of them) decided which fork would be the valid one, and the choice was to comply or be left behind. The developers also have the power to change the protocol as they see fit, giving them the ultimate power over bitcoin. As an end user, I have no power over any of that.
Devs have no chance in hell of pushing through changes unless a large majority of users agree. Unless everybody is conspiring against you in particular, you can trust the majority to have the same interests as you - to protect their own money.