Some more info on some guys experience and sources for temp gauges here:
http://forums.banditalley.net/index.php?topic=10643.0The oil WILL get exposed to temps as high as 500 deg F on the underside of the pistons, which is why there are oil jets spraying there, but average oil temp will likely be closer to 100 F, but some guys have reported temps in the 140 deg F range after sustained idling in high ambient temps.
Sustained temps above 150 F are harder on the oil and shorten the oil's life, but in our bikes, oil usually gets changed pretty often.
Use the search function for "Oil Temp" and you will find a bunch of threads.