My point here is regardless of where you draw your line you will be favouring some visitors, and not catering for others so don't get pushed into thinking that this line is set in cement - it's up to you to make the call. Personally I don't stick to the web safe palette.
Surveys suggest there's still quite a few.
Given the abundance of hi-colour sites, people surfing at 256 colours must be used to a large part of the web looking pretty poor. So rather than getting hung up on it, maybe a more realistic option is to design efficiently keeping to the smallest number of colours you really need. If there is a spec you wish to target e.g. windows running at 256 - then test it widely.