Around February 2011 I picked up an Apple 27" LED Cinema Display for my home office, as a way to help upsize the screen real estate on my 2008-era MacBook Pro. I loved it, and there was absolutely nothing wrong with it when the Thunderbolt Display came out, so I didn't think anything of it. Then I bought a 13" MacBook Air, and next thing I know, I'm putting the original 27-incher on Craigslist...
But why would I do that? What was wrong with the monitor and why trade it in? Here's my account of what you should do if you're shopping for a new monitor, and have a hankering for some Apple products.
What's Different: The biggie here is the obvious, Thunderbolt capability. Where the older 27 has three cables on its laptop connection cable (Magsafe, USB and MiniDisplay Port), the Thunderbolt only has two, discarding the USB for the super speed of the new port. On the backside, that means you've got three USB 2.0 ports, one Firewire 800, gigabit Ethernet, and of course, another Thunderbolt port.
1. File Transfers. I constantly move files around on my home network between my iMac and my MacBook Air, and doing it over Wi-Fi was painful at best. By adding the Ethernet connection, I increased productivity in the process, and made my laptop more versatile. That was a big bonus.
2. Download speeds. Pulling files down off YouSendIt and other places really was a chore on Wi-Fi, but that's a hazard of my business. Having that Ethernet connection boosted my download speeds substantially, and didn't hurt my uploads either.
3. Building a True Dock. With the three USB ports on my original 27, I did just fine with basic backups to USB drives, but now with Firewire, I can dock my faster drives too. It also means that once more affordable Thunderbolt drives become available, I can really have some high-speed storage at my fingertips, making the small hard drive size on the Air not really an issue.
For me, the Ethernet cable alone almost made it worth the switch, but if I still had my old MacBook Pro, I would've stuck with the original 27 and never thought of it again. Either way you're still getting an excellent monitor, it's just whether or not Thunderbolt is important to you.
As an added bonus, you can also daisy chain a second monitor to your Thunderbolt model as well, giving you a ton of real estate to work with.