What happened to me was an exact opposite of my friend's experience though. He was given five years validity just in time before his temporary license expired; and he did it without much irritating inconvenience.
Anyway, enough of blabbing. If you are thinking of renewing you license, here are the things you need to prepare. I'm pretty sure they are all with you most of the time.
1. Passport (profile page and visa page)
2. Work Permit (profile page and WP's validity)
3. Medical certificate (you can get one at a hospital or clinic)
4. Old license
To avoid inconvenience, have your documents copied. Make at least two copies each. Hand them over to the person at the desk and tell him or her you want to renew your license. Once the documents are checked, you will have a physical exam. Don't fret. They're just going to test your color recognition of the traffic lights. Red, yellow and green - ring a bell? A few questions here and there, and voila! You'll be out of the room before you know it. Get the documents from the examiner, sign all of the copies, and hand them back to the person whom you first gave them to.
After which, wait for your name to be called as they need to take a photo of you. Once you're done staring at the camera, you will again be called to claim your license. Pretty fast, huh? It took me less than an hour and was driving back home. Did I say you have to pay 300 something baht for both car and bike? Yeah, you have to.