The stock antenna has worked just fine for me in both the the vhf and uhf frequency ranges. So test yours out thoroughly. I can easily hit a repeater that is 13+ miles away from inside my house which is better than I can do with my Yaseau FY60. Still, it wouldn't hurt to have a back-up antenna as they can be fragile.
What is particularly great about these radios is their ability to be programmed outside the normal ham frequencies. I'm a member of a local Medical Reserve Corps and CERT team and was able to program in the town's EMS frequencies to both transmit and receive. But given this capability one has to be care not to break any of the FCC regs.
The link below is a post I made on Northeast Shooters See #16. It's a report of my first impressions about the radio.
http://www.northeastshooters.com/vbulletin/ham-radio/177337-uv-5r-2.html
I try to avoid purchasing anything made in China so it makes me feel guilty to buy these radios. But you can find them for as little as $49 or $59 with a speaker mic on ebay and free shipping if you shop around a bit (sainstore, nicheone, etc.) How can you beat that. I just ordered my fourth and fifth radio and expect to have them within 2-3 days. Apparently, all the good "Japanese" radios such as ICOM, Yaseau, Kenwood, etc.) are already being made in China as well so, perhaps, I shouldn't fell too guilty.