The general wisdom is that if the symptoms are all above your neck (i. e. a head cold, stuffy nose, watery eyes, etc.) and you do not have a fever or other symptoms, it is OK to run. Listen to your body as to distance and intensity. You may find that running actually makes you feel better by helping to clear your head. However, if you have a fever, chest symptoms or flulike symptoms, definitely rest up and do not run.
@ 5K: Ontario Mills 5K, Ontario, CA, 25:17
New Balance Palm Springs 5K, Palm Springs, CA, 24:32
@ 10K: LA Chinatown Firecracker 10K, Los Angeles, CA, 52:15
I agree....if I just have a stuffed head/runny nose I'll keep running. If I'm running a fever or have chest congestion I cut back and rest. For me getting outside and running when I have a stuffy nose actually helps a lot a I usually end up feeling better faster because my nose runs every time I run regardless of me having a cold. Just take plenty of tissues unless you plan to snot rocket!