It could be the oil switch misbehaving, but chances are if it works normally
for other modes, it's working right. 
And the if light only comes on a hot idle, Oil pressure could be lowish at a
hot idle. 
The only real 'right' thing is to put an oil pressure gauge on it and see
what the real oil pressure is. 
Lacking the means to do that you could try another OP switch. 
But it's really better to check it with an OP gauge.

If you Really want to learn something about the condition of the engine,
send an oil sample to an oil lab for analysis.
That'll tell you if there's excessive bearing metal in the oil, or if it's
fuel diluted and so forth.  
If you are 'really' taking car of an engine, like say in an aircraft, you
get an oil analysis about ever 20K miles or some interval that will give you
an indication of how the wear is progressing. 
Scott
www.turbovans.com 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Zoltan Kuthy
Sent: Monday, February 25, 2008 5:44 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Oil light comes up, 1.9 engine

Hi guys,
I wonder if it has to be serious when the oil light comes up at idleing.  I
have 20/50 oil in there.  Engine was reconditioned by VW Canada about 70k
back.  Could it be the oil switch misbehaving?
Thanks to all.
Zoltan