As long as you use the zerotrust method i.e. have the private keys yourself then they're fine.

But imo people shouldnt worry too much about bitcoin security - its far more secure than nearly all other forms of online transctions e.g. Paypal, moneybookers. The main problem is the flucuating exchange rate...

But this doesnt mean you can then use your bitcoin client on a comp which is used by other people who moght get it infected - still use a livecd.

The main problem though is that you have to trust the liveCD to not suddenly become infected...