I use CS3 and print with an Epson 9600 on Semi Matte paper. I have light areas on my prints (mostly gray skies) that look evenly colored on screen but when printed show artifacts (such as uneven colored areas or white spots) that weren't visible on the monitor.
The monitor is calibrated and I am using soft proofing from a profile I made.
I have learned to live with some colors on screen not matching my prints :( , but these artifacts are unpredictable. Anyone faced this problem and found a solution?
Thanks!!!

Well it sounds like you need a better profile to be made. I can think of nothing else, since you say it is the only areas that don't print well.

I'd second that... either a bad profile, or you're sending the print incorrectly to use the profile you have.

Try running a totally different paper, like Premium Luster. Make sure you're assigning the paper profile in Photoshop, and turning the Epson Color Controls off.

Another thing I do all the time is to print a step wedge... That lets you see exactly what the printer is dong to every value from 0-255, and if there's something weird happening you can see it.

I made one up, it's here: http://www.teddillard.com/graphics/step.jpg

There's also a vid I posted on the YouTube showing correct color management procedures sending to the printer in OSX:
http://www.youtube.com/watch?v=nlccFMPZxQs

The one fairly remote possibility is that the heads need cleaning... try that too.

Thank you both! I will try out those suggestions this week.