This is my first time posting, but I'm happy to be able to contribute to the forums on this topic, because the research I did before buying my droid x was primarily done through this forum. I went through this debate for a while. In fact, I ordered a droid incredible, which was set to ship on July 14th, when I called to check it's status, they told me it was delayed again, so I waited on line at the story on the morning of the 15th to change to a droid x.
My experience with the incredible doesn't go beyond playing with it for about 10 minutes in the store, but based on my understanding of the two devices, I'm happy with my decision.
Most reviews leave the deciding factor as the screen size saying that if you don't mind it being very big then you'll appreciate the screen size of the x. I have tiny hands, and I can tell you, the droid x is a very manageable size.
There's four things that I can directly think of that I wish the x had that the incredible does have:
1) The ability to pinch and see all 7 home screens at once. It's not a major feature by any means, but if you feel like you'd get very frustrated swiping back and forth, it's something to consider.
2) The camera on the incredible has a lot more fine-tuning features (like contrast and saturation). Mix that with the fact that it also will be getting 720p imminently.
3) Scenes. I'm not sure I would actually use that feature, but I do know that it might be useful to have one scene for while I'm at work, and another for while I'm on the train.
4) Sense ui has you unlock the phone by swiping down, while motorola's ui has you swipe across, no matter the size of the phone, I've found that swiping down is easier.
Having said that, as I said before, I'm very glad I got the x. Here's a few reasons
1) Though I haven't used the Incredible to make a call, it's my understanding that clarity is better on the x (the noise cancelling mic helps with that). I've never heard a clearer phone call than the ones I've had on my x
2) The dedicated camera button is actually a pretty important factor. The best camera is not just the one you have with you, it's the one that you can get ready instantly.
3) I love the big screen.
4) While verizon clearly hasn't given up on the incredible, the X is it's flagship device, and that means verizon will be better equipped to support you with any trouble that may arise from a droid x, than they would with an incredible
5) though this will eventually be available for the incredible, swype is the coolest thing ever, and i like having it NOW, instead of waiting till i get the incredible, and then waiting till the beta reopens.
6) My battery life on my x has been pretty short, but that's probably because i've been way way overusing it (it's my first smartphone), but allegedly battery life on the incredible is worse.
7) At this point getting froyo sooner appears to be a wash, but it may be a different story when it comes time for gingerbread
I don't want to go into any more detail because I'm not sure I'd be demonstrating contrasts between the phones. One pet peeve i have about the droid x (that I'd love resolved or directed to a relevant forum post) is that once in a while when i link contacts (linking a phone number to a twitter account) the twitter account's name will be the display name. I can still search for any part of the name, but the display name is still the twitter account.