Location of system databases - thoughts?

Hi

I am currently doing a system audit on our SQL Server estate.

One thing that has provoked thinking is the location of the 3 system databases master, model and msdb.

All SQL instances have them currently on our C:\ drive.

I distinctly remember that other organisations I have worked for had system DBs strored on the SQL data drives or stored on their own LUNS - which got me thinking about a few questions:

1. are there any advantages or disadvantages to having these system databses remaining on the same drive as the OS?
2. if system databases are stored on the data drives (ie, the same drive as all/most of the other mdf files), will this impact on each other? If so, how much?
3. are there any business cases where the best practice is to have these system databases on it's own drive space?

This is just a few questions to get a feel of other user's esxperiences on this matter.

Any comments would be appreciated.

Thanks in advance.