I do not think the issue has been fixed on recent devices. That is what was thought at first (or rather assumed because Nokia never said they had fixed the issue). However, if you look at the huge usb port issue thread there are recent owners who are now getting this problem. There are also old owners who developed the issue, received a new n900 under warranty and then the new one subsequently developed the issue.

As for it being simple to fix the usb port when it goes faulty let me use my experience as a word of warning for you. I bought my device in the US but live in the UK. When my port stopped working Nokia refused to fix it in the UK. I did not want to send it to the US and be without my N900 for some time (by the way Nokia have said no replacement till 2nd week of November which will be over 2 months after I sent it to them - great customer services eh). I took the N900 to 2 different phone repair shops who were sure they could fix it. They each held the device for 4 days each but had no such luck fixing it. So be aware that not all faulty usb ports are equally faulty. Some have only a minor issue and can be easily fixed. Some are so faulty that they cannot be fixed.