Unless you need some special encoding that compressor 3.5 can't do, I would not "upgrade" to version 4. I bought the new version after FCP X hosed my version of 3.5 thinking it would solve my problem. It only created more problems for me. (BTW, I was subsequently able to resurrect the 3.5 version with compressor repair and doing a bunch of other stuff!) The new version has Apple Qmaster incorporated into it which on the surface looks like an advantage. But I have not been able to get it to form a quick cluster despite numerous attempts. I have "spoken" to Russ on the forum here and he can't figure it out. I have spoken several times to a seemingly knowlegable Apple care specialist- they can reproduce my problem but they can't fix it either. Consequently, encoding is much slower in Compressor 4 vs 3. If compressor 3 is doing what you need it to do, stick with it. If it ain't broke, don't fix it!!!!!