That's trivial to do with little snitch.
It's not trivial unless you have a lot of network, sysadmin, and OS X background. You have to think about a lot of issues of what to permit, what to deny. Then you still get alerts and have to research the things that want access.
I'm reluctant to deny unfamiliar system apps in case I break something and later have to spend a half a day tracking down mysterious behavior.
The developers of Little Snitch have this knowledge. They could create presets for common situations.
The only preset I want is "maximum privacy while user initiated outbound still works". I'd be satisfied even with cookbook step-by-step instructions for such a preset.
Luckily, that's exactly what they're doing for v4. Hooray!
Using little snitch to "Deny All except Safari Outbound" is exactly the same as working offline, except that your web browser now works. No Networks/Sysadmin/OS X experience required. By and large, the largest and most annoying culprits on my systems are the OS X system utilities doing background updates, syncing photos, etc.... Ironically, they are the ones I most want to shut down when I'm not on home WiFi.
Plus, if you have 15-30 minutes one afternoon, it's a great way to get insight into what your system is doing, and gain some (small) amount of comfort that you know what's going in/out of your system. Well, that is, everything that isn't bypassing the kernel in the first place.... :-(