+1 to Shawn and Serg... it all depends on where your guitar is, and where you want to go. I have one guitar that I swapped the import trem out to make it sound less brash, like Shawn mentioned, and it worked well. Another guitar sounds ace with the import trem and I don't dare touch it.
Functionally, if it's set up and maintained properly, I've not noticed any problems. More often than not, problems with guitars equipped with the import trem are actually problems with the nut.