I'm definitely interested in the Thunderbolt. I'm getting increasingly frustrated with my fascinate...unreliable email, unreliable notifications...unable to hang up calls at times, freezing. I keep trying to be patient for Froyo which everyone says isn't that big of an upgrade, but the little things the Fascinate does NOT do are what bug me. Such as pause audio when a notification comes in. Or the ability to actually, truly lock my phone for security reasons. Or get facebook push notifications...not to mention the apps out there now I'm interested in that only run on froyo.
For me, rooting my phone isn't an option. I can't get my work email if my phone is rooted. So I can't play with all the different roms and kernels to get my Fascinate working like it should have from day one.
Having said all that, I'm not happy the Thunderbolt is a 4.3 inch screen. I do think the 4 inch Fascinate screen is the "sweet spot". And I'm very concerned about battery. So while I am very interested, it's definitely going to be a case of I have to see it in person and hear what is going on with the battery first.