Didn't yet feel the need to try it. For developer testing, I'm quite happy with JUnit; for acceptance testing, I prefer something that looks more like something business people can understand, for example FIT/FitNesse.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus
Umesh, I'm in the same boat as Ilja. I am happy with JUnit for unit and integration tests. For end to end GUI tests, I prefer to use a browser based tool. For end to end back end tests (like file processing), I am also happy with JUnit.
TestNG has a couple "features" that scare me, like test dependencies. I don't want the ability to do that! While I'm sure it's possible to use this in a good way, I view it as giving you rope to hang yourself. Most of the other features seem like they have the potential to be useful, but don't address a need we have at the moment.