I agree with most of the opinions already expressed. I have a PowerMatic 3520 and am real happy with it, and have basically put about 1,000 hours into it resulting in 400 pieces, mostly just rough turned. (Okay so I'm not real fast).
From a design standpoint they did a decent job. However, a lot of little flaws get tiresome when you put a lot of time into the lathe. Would have been nice to have the following options:
1) 3HP motor - I turn some biguns sometimes and this would help keep it from stalling when roughing them. The 2HP is a fine motor and smooth as heck but I would have paid for a 3HP upgrade.
2) Built-in vacuum port into the headstock. I made my own vacuum setup and it works fine, but built-in is often better.
3) One or more index wheels that can be attached on the outboard side. I made my own (see my picture gallery). I wanted the room to get around on the inboard side so an index wheel on the inboard side didn't work for me. Rube Goldberg would be proud...but it works.
4) Minor design flaw - lack of hands free spindle lock. Some folks have posted how to resolve it, but for the price it should be part of the base lathe. With the base lathe and no modifications you have to hold a finger on the spring loaded lock button. Pretty lame.
5) Minor design flaw - the camlocks on the tailstock and headstock take some muscle to lock if you have a polished lathebed. Maybe the higher end models have better design here. Next time I turn some wet oak, I'm just going to let the crust sit on the bed so it will lock easier
6) Minor flaw - toolrest cam lock has a lever that is too short. Maybe this is better on high end models. I modified mine with a longer custom shaft, and 200 hours later I sheared the bolt. ...one of my biggest gripes about the lathe.
7) Option to add-on an extension so you can do large pieces (>20"). This could be setup so you slide the headstock to the end, and the extension would hold the harp so you could turn 30" pieces etc. Not that hard to design, would maybe cost $200-$300 retail.
8) The tailstock weighs about 50 pounds. It's manageable, but you don't want to take it off every hour or so
If you get the 3520, I would recommend ordering the bed extension. About $120-$150. I never used mine but someday I will want it, and it doesn't take much space to store it.
Just a lot of my opinions for what they are worth. And if you get down to it, I'm a pretty happy 3520 owner!! It's a great lathe. You should also look back in this forum about a month or so, the 3520 was discussed.