Sure, digital zoom does not cause any increase in the quality and detail of the subject of the picture, and decreases the quality of the picture overall. However, if you start out with a higher number of megapixels (more detail/quality), some optical zoom can be used before the quality drops below your standards.
For example, say you want to take a picture of something far away. The quality of how well the picture shows your subject can be "measured" by how many pixels in size your subject is on the picture (given all else - like noise - is equal). Say you have a Panasonic FZ1, and your subject just about fills the screen when you use the 12x optical zoom. In this case, the subject is 1600 pixels across. Now say you have one of those super-nice Nikons with 8mp and 6x optical zoom. The 8mp image is 3200 pixels across (twice as long and twice as tall as the 2mp image). If your subject filled the screen with 12x zoom, it will take up 1/2 the picture with 6x (assuming the wide-angle-end equivalent focal lengths are the same, or pretty similar). This means it will be, again, 1600 pixels across.
In the end, what matters is how many pixels the camera fits per degree of your field of view. The pixels per degree are proportional to the square root of the number of megapixels (FOUR times the magapixels means TWICE as many pixels per degree vertically, and TWICE as many horizontally), but it is proportional to ONE TIMES the optical zoom (TWICE the optical zoom means TWICE as many pixels per degree vertically, and TWICE as many horizontally).
In other words, because the pixels are about AREA (two dimensions) and the zoom is about linear proportionality (one dimension), the optical zoom has a much greater effect on the detail of something far away - you need a lot more megapixels for the digital zoom to have the same effect.
In other words, twice the optical zoom gets you as far, detail-wise, as four times the megapixels. Or 1.4 times the optical zoom gets you as far as twice the megapixels.
So go for the optical zoom. I'm a very happy Panasonic owner myself, having started out with the FZ1 and now using the FZ10.
And for more information, check out