Hi, today I connected my brand new Ethernet Shield to my Duemilanove and, to my surprise, the shield grew very hot very fast!
The hot part is the WIZnet million-pin IC.
I grabbed my Digital Thermometer and, to my surprise, it was 49ºC (120ºF)!!!
Is it supposed to be this hot? The only thing it's connected to is the computer - through USB!!!
I'm kinda freaking out, guys, I don't wanna blow up my shield... It was NOT cheap. 
did you assembled it yourself?
No, it came fully assembled. I don't even think it's sold as a kit...
Look at it: who would want to solder this themselves? link!
I have two of the original Ethernet Shields (same Wiznet chip). They run a "little" warm. My uncalibrated fingertip says the surface of the IC package is probably somewhere around 40-41C. Not hot enough to make me uncomfortable.
This is with or without connection to my Ethernet LAN.
Regards,
Dave
Same here, my old ethernet style shield runs 'warm' to the touch. The wiznet is a greedy little begger and consumes about 150 mA, at 5v thats 0.75 W, about right to mildly warm the chip. Again, my fingers are uncalibrated 
Fingers are quite well - with a little bit of practice you can distinguish: below 10, around 20, 30, 35, 40 , around 50 centigrades.. Also 80 degrees is simple as this is where proteins co-aggulate....
Mine got around 50°C too. But still lives.
Thanks guys.
I thought there was actually something really wrong... Oh well... :