Wow, here we are in October and still no definitive solution to the issue. I have the DX and suspected the Facebook app is the culprit and have been shot down by a Verizon tech and some other forum members in some of the other Droid forums.
I noticed that it takes awhile for my contacts and texts messages to load up the names, pics, and threads. Once they are all fully loaded my DX works fine. If I try to make any other moves while it's loading then several different problems occur. The loading process takes several MINUTES, not seconds, for me and my DX is only a month old. Once I downloaded the Froyo OS upgrade my DX's performance picked up quite a bit and even the contacts and text messages were responding quickly, however, ONLY the contacts and text messages were slower than anything else on the device. Now I'm almost back to where I was while I had Android 2.1 software loaded on the device.
I have over 2k contacts between my phone, fb, and twitter accounts. I believe the OP that this is an isolated issue for some of the DXs out there, not all of them. Facebook is actually pretty important to me as I personally deal with a lot of people on my friends list so deleting it or setting it to not sync to my contacts is not an option for me. Besides, this device was developed with this in mind.
Task Killer was the 2nd app I downloaded to my phone so I have to disagree that that Task Killer is a fix to this issue. My next step is to now call Motorola, report the issue, tell them about this forum, and get a case number. It seems not many people understand how big technological companies such as Motorola and Verizon handle these types of issues and resolve them. If you don't call, yes YOU, then Motorola and Verizon will not acknowledge a problem with these devices since YOU are not complaining about it, they will assume you can live with the issue.
The DX is a great device, but when you can't use it to contact people what is the use of it? It might as well be anything, but a phone. With the official release of 2.2 on Sept. 22nd Motorola apparently didn't and still doesn't know of this issue. I say this because the latest official software does not fix the issue we are all dealing with in this thread. So with this in mind people, please pick up your phones and call Verizon and then Motorola...tell them you want to report an issue and get a case number. Eventually, with enough DX owners complaining they will be forced to formerly address it as a "known issue" and develop a fix.