it depends on where you live. I find that first-class mail to/from Los Angeles is ridiculously slow for some odd reason. My sister in law in Texas once sent us a POSTCARD that took 3 WEEKS to arrive to us in LA! (it was an invitation to a party, and we rec'd it after the date of party had passed, lol) Also, once we mailed a check from LA to the caterer of our wedding (in another state), and it took four weeks to arrive (again this was just an envelope!) it was all very bizarre... i have lived in several cities and never had this problem. THe issue is never with fedex, ups, or EMS or any of the "accelerated" mail types, only with first-class USPS mail.
anyway, 5 days for something that is going across the country is not that long IMO. especially now with all the hurricanes, storms etc in Houston area, there may be delays due to that. I'd give it 10 days before getting worried.