Is mp3 transfer for Windows iTunes / iPhone 4s slow? I'm about to buy iPhone 4S, I'm curious about how fast is mp3 transfer (since I like a lot of music). And I'm using Windows. Is it a LOT slower than common direct USB transfer like on mp3 devices or is it "ok" speed?

And I'm using my own mp3s I have on my HDD.
Speed is not an issue between iTunes and an iPhone. You can copy gigabytes of data (music, film,...) within minutes, just like with a standard USB-to-desktop connection on Windows or Mac.

Major advantage: the synchronisation makes it even faster if you only change a part of your music: it only copies the ones that you added for the first time: no more duplicates!