1) Do you find the pedals too small (surface area-wise) ?
Not at all. I have a size 7 foot... and my boyfriend uses them and he wears a 10.5. He doesn't have any issues with the size of the pedal. Really, the size of the pedal won't matter if you have a good solid bottom on the shoe.
2) Is the large amount of float really hard to get used to and/or bad when out of the saddle?
It's easy to get use to. The first couple of times I was a little freaked out and now I don't notice it at all. I even stand up on them climbing hills no problem.
3) Is it really impossible to use the cleats if they get at all dirty?
Oh yea. DO NOT GET MUD stuck in the cleats. Which can prove to be a challenge at bike rallies since you typically have to walk into mud to get your water bottle refilled. They do have cleat covers you can put on to protect them when walking around, but they always fell off when I used them. Now days I just walk on my heels around dirt and mud.
4) Do the cleats really wear out super easily?
NO WAY. Well, I have my first set of pedals that I bought back in May 2005 (5,000 miles on them). They work great, still. In fact Speedplays are better with age. When they are new they are a bit hard to get in and out of. Once broken in it's like butter!
I did buy some new cleats... but only because I bought another set of pedals for a second bike and I wanted the new cleats put on my shoes. They were not worn out though. I could have still used them. Although, the screw head had been worn off! 
5) Have you ever clipped out accidentally?
Nope. Not at all. The scary part isn't getting out typically... but NOT being able to get out...
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"