Yes off course but if you're active on different forums and they all have different rules you end up converting your photo for each forum and that's quite a lot of work if you've several photo's.
It's not just the converting but also the uploading and linking.

For forums i mostly use 900px with high compression and i've heard nobody complain about it.

Wouldn't you get almost the same effect with larger formatt camera's?

But you wrote in anotehr comment that there is a coating on the mirror, so the silver in the mirror never gets into contact with the dust to begin with so is the coating anti-static as well?

But that's not the forums fault, it's the web-browser that you're using that is making the mess

If you use chrome, opera or firefox then everything is okay but if you use IE you need to look at the compatibly mode.

The K10D at least doesn't have that option so it wouldn't work on all camera's and Jonathan is using a K200D which isn't that much younger.

Still no matter what, you should keep an eye on the white balance with these sort of things.

How do you know?
I know the filter on the sensor has an anti-static coating but never heard something about the mirror.

Yeah maybe.

Btw are there liquids you can use to make the mirror anti-static?
I mean the mirror moves up and down with every shutter actions so if it would be anti-static i doubt any dust will be able to stay on for long...

Uploading or linking?

If you upload a photo here the Gallery automatically resize it right to 800px?

As for forum posts, if you link a photo there it's automatically resize to 800px horizontally but it's not wise to upload full res. photos on to the web because it slows it down quite a lot and there is no need to have such a large photos.
I use 1024px or 900px on the long side and use 60% JPG quality, a higher jpg quality is not needed and will only increase the file size without gaining any noticeable details in the photo.

It might sound strange but this isn't a fix value with Pentax it actually just limits the Auto mode to whitebalance you get with Daylight.
So it might be better to use custom white balance instead.

But that's actually quite natural, light almost always come from above so some shadows are to be expected and it will actually give some dimensions to the face.