I've actually read the opposite. At the same time, it seems that there's been issues with the Fascinate drawing more power w/o use simply due to it having inferior reception to the X at times (before I excite the mob, I mean the SF isn't close to being always in par to the X's reception abilities), so it has to work harder.
I ran the DX and Fascinate side by side for a bit, after owning the X for about a week and a half, and I have to agree that the standby is longer on the Fascinate, but the DX got me more talk time. Of course this was with my particular usage. It will vary so much between users ...
I did extensive testing on the signal strength though, with both phones. As expected, the DX was better, but not anywhere near as much as I expected it to be. Even if the Samsung reported a bar or two less, the call quality remained excellent on both phones. I tested it in some very common problem areas, and in every single place where the DX outperformed my other phones by a noticeable margin, the Fascinate ALSO outperformed the other phones by a noticeable margin! This surprised me, and I continue to get excellent reception and call quality with my fascinate.
As far as the echo goes, if I have the volume extremely high on my fascinate, I can hear a bit of echo. If I turn it down a bit, it really does go away completely. I tested this placing calls Fascinate to Fascinate just to be sure.
And yesterday I used the GPS again. It was dead on. Locked fast. I turned on the satellite view as well, and I watched my little blue arrow (which was me!) drive around a neighborhood looking for a client's house. It was pretty funny to see an actual picture of the terrain I was on, and see this little blue triangle going back and forth, turning around, etc. I probably creeped some of the folks in that neighborhood out, but I was seriously having a blast playing with my GPS!!
I rooted the DX, and it made things better. I got rid of the crap on it, threw a new interface on it, and did some additional cleaning and tweaking and customizing. It is a fantastic phone, and at least I personally would be right as rain with either. I call both phones a tie overall, but the two things that swayed me finally in the direction of the Fascinate were readability in sunlight and ergonomics. The DX is dreadfully uncomfortable in the hand, and difficult to operate one-handed. The Fascinate feels much more natural and ergonomic.
And I don't know what some of you guys are doing comparing this things in the sun, but I cranked brightness to max on both phones, and the Fascinate was a little more contrasty out there. It might not have quite the brightness, but because the blacks are so black, even with brightness cranked all the way up, the contrast of the phone makes it really easy for me to read in the sun. If you turn down both phones' brighness all the way, the Fascinate also beats it in visibility.
Text is sharper on the DX though.