I'd say you go for the camera that feels best in your hands. The looks to future customers are not all that important, I think, because, as popo wrote, you portfolio is what matters. And many customers won't even look at what camera you're using, as long as the results are good enough, the brand doesn't matter.
There's been more discussion about the noise issues lately. If you avoid using high ISO's (e.g. 1600), you'll get results that are good enough for most situations. Only if you make very large prints or do a lot of cropping, using high ISO values, you may want to look at another camera, meaning, a non-entry-level DSLR like the 40D or even D300.
Sony's future in the professional sector looks good to me. Very high quality G lenses, but especially the Carl Zeiss glass! There's not a whole lot of info about the A900 (results-wise), but it shows that Sony is serious. There goal is to one day become market leader in the DSLR-market, so expect to see a lot more professional gear in the future.
The noise problems, I believe, will be solved in the future. Sony manufactures a lot of sensors for Nikon too, and they seem to handle noise perfectly, based on the same technology. So Sony will start thinking about that more and more.
I hope you stick with Sony and wish you a lot of luck going professional!
- Bjorn -