Many electronic devices have heat tolerances far outside of what is 'hot' or 'warm' to us humans. If you feel that uncomfortable with it either hope it dies within the warranty period, exchange it for a new one at your local store (if you purchased it from one) or call up Linksys to complain and see if they'll RMA it for you.
Without voiding your warranty those are about your only options.
That's normal for that router, but still prob not good. I have mine lifted about an inch of the ground with some diy "feet" i made from thread spools. Now its as cool as my WRT54G used to be.
Solution: put it upside down. linksys chose form over factor. Heat is supposed to go up. the heat vent is at the botom and heat rises up and heat up the router.