Let me go into some more detail about my experience and you can make your own decision on what to do. First of all, go download Astro from the market (if you've not already) and backup all your apps.
My phone was doing as you described and taking a very long time to load messages, switch between contacts, load address book, calendar, etc. It was also force-closing a lot on various apps and even rebooting at random. I stripped my phone back down to the bare apps and it was still loading slow. At the time, I also think the Facebook app had a major glitch with synching your contacts and this caused some problems. The final straw was when I decided to remove the FB app. The uninstall stopped during the middle and never made any more progress. I had to do a battery pull to get my phone to respond. When I put the battery back in, I was looking at the red eye of death and it would never do anything else but stare back at me (for over an hour until I got to the VZW store). They reset it, and did a factory reset so at least I was back in business. Phone was speedy again. I didn't install any apps that evening but did link it to my gmail account (1,500 + contacts). The next day, my phone was already starting to be sluggish again. It crashed multiple times and at that point I called Tech support and they ordered me a new phone. I've had no problems with the new one like I did with my first phone. I talked with others on forums that were having the same problem and we never could diagnose it. I was one of the first to get the phone on launch day so it might have been a bad batch at the beginning?
If you want to wipe your phone and start from scratch you can give that a whirl. Just backup your apps first for easy reinstall later. I also don't have my twitter account synched with my phone. I use an app instead and I think Twitter was slowing down my contacts a little. Keep me posted...
