DataAssist uses almost entirely server side code.... we will be testing on IE8 with all products, but the last update of DataAssist may have been before the IE8 release.
Having said that I am confident that DataAssist does in fact work with IE8. Do you have a sample url where I can debug the problem? What trigger are you using? It may have something to do with your security settings in IE8, because nobody has reported an IE8 issue before and I personally use IE8 and DataAssist all the time.