WOW! I've never given that much thought to how I perform ukemi. In fact after reading this, I'm confused a bit and may never roll properly again.
Ok, seriously. I prefer to use some degree of arm contact when rolling forwards for basically the same reasons as Ian. I feel more comfortable and in control by rolling in that fashion. Although, rolling forward without using your arms does look pretty neat. I've really got no clue as to whether or not my toes are curled or not, I've never even thought about it before. Taking a guess here, I'm going to say that I keep my feet flat. I'll have my wife watch me roll to find out for sure. Have a good day!