We have a 61" Samsung DLP. In almost 2 years we have never noticed the "rainbow effect". If you didn't see it in the store (especially with the florescent lights), you won't see it at home.
We just bought a replacement bulb but have not used it yet (4500 hours on the original bulb).
I have a ~3 year old 61" Samsung DLP RP too. I've seen the rainbow briefly 2-3 times. For me to see it, I have to move my head left<-> right without rotating, something that rarely happens when watching. I'm still on the original lamp too -- haven't braved the service menu to see the hour count.
