I am using Fireworks to create my images. Many times I just save the images as png and add it to the page.

Changing the image to something else requires exporting it to another format. Bit too much work. Is png safe option and that is display proparly in all browsers?

PNG images are more then OK for web pages They are small yet hold a large amount of detail. There is really no need to change to anything else, but if you find the compression is still not enough. You could always make them jpgs Good luck! You should be fine with PNGs!

I think PNG should be limited to where you need to use a transparent background. PNGs have only recently been compatable with most major browsers... IE only supports PNG from IE7+ otherwise you have to use hacks to get them to display which slows page load. Not as big of a deal as it has been in the past thou.

Compressed JPEG is the preferrred format unless you are not using many colours, than GIF is the way to go to keep filesizes down.

I think PNG is a Web standard format. It's cool to use, if you want to deal with the bigger file sizes.