We've heard a variety of reports relating to problems with the display on Apple's 27-inch iMacs. Some customers have received iMacs with cracked or flickering screens. Others have seen their displays take on an unsightly yellow tint.
We can't say we encountered any of those problems when we reviewed the 27-incher in October. Apple also has yet to publicly acknowledge anything other than shipping delays because of high demand in an apology back in December.
If you're suffering from any of these issues, you're thankfully not without options. If your screen shows up cracked, get in touch with Apple's customer service to request a repair or a refund. For those with a flickering screen, Apple quietly released a firmware update a few weeks ago. If that doesn't solve the issue, Apple is reportedly working on yet another update.
For the yellowing problem, Gizmodo got its hands on an internal Apple tech support memo that you may find useful. According to the note, you'll first need to convince the support rep that any yellowing you see isn't because of standard LCD variability. Then, similar to receiving a cracked screen, you can either ask for a refund, or wait three weeks for a repair.
Without access to accurate rate-of-return information, we can't comment on your odds of receiving a 27-inch iMac with any of the above problems. If anyone has such data, please feel free to share it with us. We've also seen no reports relating to problems with the 21.5-inch iMac.