To the OP, the one area where Motorola devices tend to shine is in call reception and call quality. Plus features like noise cancellation make this the device to choose. Plus Moto's are generally built like tanks. You'll see this right away when picking them up. I prefer the metal case of the X as opposed to plastic, but some like the light weight.
Some may like the DX screen, others may perfer the fuzzy text and oversaturated color screen of the SF. Yes, it does pop, but the next time you can't get white to look white, you'll get tired of it quickly.
Hardware wise, both devices are very close. They share basically the same processor, but the SF has the better GPU. Sill, for everyday use, there's no benefit, and a battery detriment to that extra power.
Web browsing battery performance is approximately double for the Droid X. Movies are similar. Simply stated, you'll be able to watch longer or browse longer with the X.
Interface is a mixed bag, some like or hate Motoblur, some like or hate Samsung TouchWiz. Touchwiz looks prettier, but blur is more functional. Plus, if some are complining about lag on the X, take a stroll over to the Fascinate forum and look at all the lag fixes they have if you root.
Both are very capable devices. But capability on paper only matters if it works. A device that can't hold on to calls, has poor reception and GPS capabilities is not going to please many consumers.
You want to switch for a reason, and you won't be disappointed to get those functions that actually work.