> Could anybody tell me what the recommended minimum track widths are for
> different current values. A general case formula or rule of thumb would be
> great but specifically around 0.4-0.5 amps.

I use a nice calculator that UltraCAD corp. has made available.  It will
solve for tracewidth, temperature rise, ampacity, width and thickness of
copper.

http://www.ultracad.com/pcbtemp.zip

-d