No umbrella while at Disney for us, I go get the $1 ponchos in the camping section at my local Wal mart, they are great for emergency's, as I carry one for each member in our party, I put it in the back pack. That being said, we have never had to pull them out, the one time it did rain were were browsing Innoventions and by the time we got out, it had stopped.
Umbrellas are dangerous, I can not tell you how many times I have been poked by others who do not pay attention to what they are doing (not in parks but other places).