I have an unlocked Milestone 2, which I rooted using z4root. I downloaded z4root from the internet as it's no longer available on the market. The first time I ran it, nothing happened after 30 minutes (the wheel was still spinning), so I applied the usual IT solution: switched it off, took the battery out and put it back in, turned it back on and re-ran z4root. This time it worked in just few seconds. Ah, the rigourous scientific approach underpinning IT! Searching the web I noticed I am not the only one with a similar experience. Anyway, it worked and it was quite easy. I understand z4root also has an option to unroot the phone but I haven't tried that.