Yes, there are differences in approaches between the two companies, even though they often use the same sensor and create cameras that look similar (e.g. GF-3 and E-PM1).
Panasonic requires lenses to have image stabilization; they do not include it in their bodies. Panasonic tends towards more video capability, especially in a few models such as the GH-2 (and the GH-1 and GH-2 have been hacked to add even more capability). Panasonic has models with built-in EVF (e.g. G3, GH-2). Panasonic has models with higher megapixel counts (up to 18mp at the moment). Panasonic has the only models with fully swivel LCDs (e.g. G3, GH-3). Panasonic has several models with touchscreen interfaces. Panasonic JPEG rendering has improved in recent models, but still lags state-of-the-art. In the US, Panasonic has been abysmal at delivering product quickly, and has minimal dealer support.
Olympus uses in-body image stabilization, thus can stabilize any lens. Olympus' video capabilities tend towards automatic and fewer feature choices. Olympus supports off-camera flash in some of their models. Olympus has external EVF for most of their cameras, though those EVF models are not as good as the Panasonic internal versions. Olympus only makes one model with a tilt LCD (E-PL3). Olympus JPEGs tend to appeal to users more (more contrast, better color, better noise/sharpening choices).
In the beginning, Olympus had more compact lenses than Panasonic, though that is now starting to even out, and, of course, you can use an Olympus lens on a Panasonic and vice versa.
There really isn't a bad choice between the two, only a lot of small differences. I'm a firm believer that how comfortable you feel with a camera will be a large factor in how good the results you get of it are, thus I strongly encourage you to try both and pick based upon that if there is no single other factor that tilts the choice. For example, if you like eye-level shooting, the Panasonic G3 is a more comfortable camera than the Olympus E-P3 with the external EVF.