It depends on your threat model. If you're worried about big organizations who really really want to see your data, they're probably going to see it. The hardware and software to do this is generally available to ISPs since they're required by law to provide for "Lawful Intercept" in many jursidictions: http://en.wikipedia.org/wiki/Lawful_interception And unfortunately, the implementations by the router companies are pretty bad, as Forbes notes, so hackers may get access also.
Then there are all the other possible attacks, like DNS cache poisoning, phishing or routing (BGP) attacks, on connections that don't have the good endpoint authentication that SSL provides. See e.g. how the Dalai Lama's organization was hacked. Even security gurus figured they would be vulnerable to that kind of attack.
If no one (including insiders at your ISP or near your destinations) cares about you, you'll probably not be snooped on unless your local network is a convenient and easy target, like most wireless networks are. But if sufficiently savvy and persistent folks (even individuals) do care, beware.