I wanted to share my experience with my laggy Droid X and the only thing that fixed it, in the hopes that it might shed some light on the mystery lag.
I rooted it a while back using Christim's guide from September and it worked perfectly. I really enjoyed doing it in the terminal emulator. Thanks Christim! I had every intention of trying different ROM's so I backed mine up on January 4th using Clockwork. This was my saving grace because I had to use it last night to restore my DX.
Other than the actual rooting, my DX is essentially unmodified and running Froyo 2.2.1. A couple nights ago I was messing around with c:geo with GPS active (a geocaching app that integrates with Google Maps) and I fell asleep. I had it plugged in so it ran all night. When I woke up it was extremely hot. Everything from that point on was super laggy. Shaky screen transitions, text entry lagging behind up to several seconds, notifications sometimes reappearing 2 or 3 times from incoming texts, the calendar widget would disappear and reappear randomly and I would keep dropping my cell signal and it would rotate through no signal to 1X to 3G.....it was so annoying it was essentially unusable.
I started uninstalling apps, I cleared the cache, I moved apps from the SD card to the phone, I disabled animations, I did multiple factory resets all with no results. I did not have a Facebook account linked to my contacts so it wasn't that. I rebooted with the SD card removed. I tried every tip and trick mentioned in multiple forums and there was no improvement of any kind. I had become convinced that somehow there was hardware damage from running the GPS all night.
Then I remembered about my ROM backup and figured I had nothing to lose so I loaded it up and to my complete surprise, it worked like it was brand new again. No lag of any kind. I had been using c:geo for months with no problems so I don't know if it was the cause. I didn't have anything on auto-update as far as I know.
Because the ROM backup restored proper functionality, I can only assume that I was in fact experiencing a software error/bug of some sort. I have no idea what could have happened. If I hadn't been rooted and made that backup, I can only imagine that I would have had to get a replacement. Has anyone had a similar experience or have some insight as to what might have happened?