I'm planning on doing the 5K during next years Springtime Surprise. I'd like to do every distance over the course of several races (not Dopey!! haha). I knocked out the 10K this year for Marathon weekend.
My one complaint about runDisney events is how they cut into my trip - spending time at the Expo, going to bed early the evening before, waking up early the next day/running/recovering, etc. While a 5K isn't challenging for me (and I likely won't stop for any character greetings because of the huge lines), April seems the best time to do one. I don't know that I want to run more than 3-4 miles in Florida in April.