Question: In my silverlight application I am trying to get the actual dimensions of a png image that I am loading into an image control. 

After scowering through the internet for a while I learned that in silverlight 3 there is an attributes called PixelHeight and PixelWidth.

So I was wondering if it is feasable to upgrade to Silverlight 3 since it is in beta stages, don't want my application to be suddenly riddled with errors. 

Note I am doing this project for a school assignment so versioning of silverlight doesn't really matter.

Answer: 
Even though Silverlight 3 is expected to be backwards compatible to Silverlight 2, expect to run into some issues. The conversion wizard does a good job but you cannot completely trust it.

why don't you try it and see if you it is seemless in your case?
It looks like Silverlight 3 will be going RTW middle of next month (July 10th has been mentioned), so you might want to wait till then and pick up the released version.

For my part, I have found the beta completely stable.