I believe you can do this, has anyone any experience? I seem to remember I've got to change shield gas from Argoshield to Stainshield, how do the welds turn out? Comparable to MIGged mild or different? Any pitfalls to avoid?

It works ok provided your mig is capable of fine adjusments and is of reasonable quality. It is not as neat as tig and you get lots of distortion in thin material mainly due to the higher deposition rate of filler metal you get with the mig.
Just my thoughts, I've done it but not lots of it.
Bruce

Have a look here:
http://www.locostbuilders.co.uk/viewthread.php?tid=35956

I asked my local gas supplier about this at one time and there was a special mix for welding stainless. I think it was the normal co2/argon with a bit of helium. I have the info here someplace and will update this when I find it. I have welded stainless to mild steel using co2/argon with good results. It was only a bracket on my glass bead cabinet.