I saw the 'z4root' application on the Droid market just now. Is it safe to use on my Samsung Galaxy S? Anybody used the Z4ROOT program to root/unroot his device ? Can I use it on my Samsung Galaxy S phone ?

Is it a real root / unroot process ? I am a developer myself and know how much damage you can do on a computer if you have too much power and too little knowledge.

However, a true root / unroot program seems ideal. That way I can root the device if necessary (f.i. to grab a screen dump or whatever) and unroot the device immediatly afterwards (until such time I really know what I'm doing - if ever :)  ).
I've rooted my SGS with z4root and it was a very smooth process! I can highly recommend z4root!

And while you're at it, continue with installing One Click Lag Fix to make your SGS lag a lot less! I did it, and haven't looked back since. OCLF is made by the same guy who made z4root, but for some weird reason, OCLF can, by itself, only root pre-froyo phones. But that's not a big problem, you just need 2 apps instead of one :)