I have a MIM 2002 P bass special deluxe series (p/j). I can tell you the differences between that and the US version.
It's made of the same wood as an american standard p bass (although you only get one choice, alder, wheras the US one, you can choose ash)
It's got the same neck and same electronics (caps, pots and wires) as a US standard.
Thats about where the similarities end. Except in the shape.
The US version P bass special (p/j) has active electronics. The MIM is passive. Although this difference is only relevant to this model.
All MIM pickups are well... MIM. full stop. They're no where near as good as the US ones. Same goes here.
All of the chrome hardware is also MIM. The tuners are ok, the stock bridge is like a US, ie, flimsy and crap, but the finish is not so good.
The main difference though is in the set up. They simply produce guitars quicker in Mexico than in the US, so the set up just isn't as good. This is why I think so many people are down on MIM guitars. They play them in shops and they play like dogs because they're poorly set up compared with the US. they also sound thin because the pickups are bit crap.
So my advice to anyone buying a new fender, esp a bass...
Buy a MIM. Change the tuners, change the bridge, change the pickups. Have it set up the way you like by a pro. You should set up any stock fender anyhow. Even the US ones.
You should have a MUCH better guitar than a US standard. For much less $$.
It's exactly the same guitar, but with better bits, and set up by someone who's setting it up for you, not just setting it up so it plays ok.
I paid £260 for my guitar (almost new), and with about £140 extras, I've got schaller tuners and bridge,
a fender vintage noiseless J pickup and a Fender original p pickup. It's more like a custom shop than a stock bass. and still about £250 cheaper than a US standard. (with no J pickup)
John