All this really means is that rather than the sun's orbit laying on a nice plane, the plane is slightly warped, which isn't inconceivable when you bare in mind that the sun effectively orbits an extended mass, rather than a point source.
So, the sun passes the galactic plane about 6.5 times in one orbit(according to my now triple-checked calculation), about every 37 million years or so.
This wave motion is significant(as opposed to a purely elliptical orbit) because it shows the presence of a very strong gravity pulling inwards towards the galactic plane.
I believe that the cumulative gravitational effect of the rest of the stars, dust, and galactic matter of the disc can not account for this steady motion(hence the need for dark matter). In fact, I don't think that there even is a cumulative effect, and I don't think that the locomotive analogy applies to this situation. Also, what of the galaxy rotation problem?
http://www.knowledgerush.com/kr/encyclopedia/Galaxy_rotation_problem/
It makes a lot more sense that this inward attraction towards the galactic plane is actually being done by a much more significant, dependable force. As I said before, I believe that the extreme gravity of the galactic center is not only pulling everything towards the galactic center, but also towards the galactic plane. I think that this center gravity is, in a way of speaking, being funneled through the 2-D galactic plane(sort of like the inverse of a plugged-up garden hose with tiny holes all along the top and bottom of it's tubing being swung around in a circle with the water turned on). I think this theory makes a lot more sense than dark matter.
This theory is also significant because it presents a danger zone, the galactic plane, where the main source of pulling gravity is suddenly reversed as any object passes through it. This would obviously create devastating effects for any ecosystems living on the crust of any passing planet.
Another significant fact: it's been officially known that we've actually very recently passed(in galactic terms) the galactic plane. Yet, there is an obvious margin of error in making this calculation, especially if dark matter doesn't even exist. In any event, the location of the galactic plane is a matter of debate. So, we could very well be headed towards the galactic plane right now.
As a matter of pure layman speculation(same as above I suppose), I imagine that earth would not feel the gravitational effect of the galactic plane gravity(GPG) until the GPG starts to overcome the effect of our own sun. And since the sun moves at 225 km per second, we would run up on the galactic plane very quickly. So the duration of changed gravity effects on earth's surface may only last a short amount of time. Although the indirect effects of this gravity change would be more long lasting, and more devastating.
Could this be a warning?
http://www.youtube.com/watch?v=5wYyqef_33I
Notice the dinosaur at the beginning of the video...