I was on the horns of the same dilemma, Droid X or Fascinate.
Background: I figured out that, except for a brief flirtation with a BlackBerry Storm, the last six phones I've had were all made by Motorola. The term "Motorola Fanboy" sounds really, really strange, but I guess that's what I was... I pre-ordered the Droid 1, and got it on release day, had it rooted the day the root process broke. There's more, but you see where this is going.
When the Droid X was announced, I asked "Where do I put my money?" Then I heard a frightening term: "E-fuse". Of course, that turned out to be something of an exaggeration, but the idea was troubling. This was followed by "Locked Bootloader".
With all this, I still wanted one, but I wanted to actually hold one before I plunked down my cash. I'm still waiting. My local VZW store, Best Buy, Costco, you name it, gets a couple in once or twice a month, and they're gone by lunchtime. I just looked at the VZW site, and right now they're saying the estimated ship date if you order today is the 24th.
So between being locked up and unavailable (okay, I'm being impatient here), I decided to go a different direction.
I pre-ordered my Fascinate, got it on release day, and had it rooted within 90 minutes (20 of which were confirming that the root was persistent). Less than two weeks later, we're on the verge of a custom recovery
This thing is SUPER light, and WAFER thin! It doesn't have that bulge on the back like the DX does. I also agree with the description that the SF is "Just the right size". My neighbor has an EVO, and I think phones of that size are actually a little too bulky.
Don't listen to much about the things people are complaining about with the Fascinate. Every new handset gets some of that, and it all gets worked out in the first few weeks.
The ideal thing, of course, would be to hold them both, one after the other, and see which one gives you the bigger smile. I tried to do that, but wasn't able to. It's hard to imagine the DX would make me happier than the Fascinate though...
And, of course, the universal disclaimer, YOUR MILEAGE MAY VARY! 8-)
You're not going to go wrong either way, btw...