A similar topic is running on another thread, apologies if my post sounds familiar.
Another one in "It did spoil our holiday" camp Im afraid. The weather was horrendous, unbearably hot in the morning and then vicious thunderstorms afternoon and evening. Crowds were sometimes so bad that even walking round became a chore. It didnt help we had two very small children who hated the storms...we would never go at this time again.
To be a little more positive, if the storms dont worry you, then stick around in the parks. The crowds disperse rapidly during heavy rain, and most rides become walk ons. If you can get to the parks EARLY, then you can get the big rides done then. If you want to see a parade, then be prepared to stake out a spot up to 2 hours beforehand.
Planning is the key to every successful WDW holiday...even in July you can still beat the negative points by being prepared. You have the advantage of lighter evening, longer hours, more shows and parades and less ride closures.
Have fun.
Allie