I was completely new to macs as well when I decided on buying an iMac (mid-2010). I was aware of the yellow tint issue but was convinced that I would get the best computer I have ever owned. And I did. Now this iMac has a little bit of that yellow tint on the bottom of the screen. However, it is only visible in those yellow tint tests and even then it does not exactly look like the color yellow -- it just looks like a warmer tone of white. I cannot see the yellow tint in normal use. If I really focus on the colours of, say, this page, I kinda see that the tone of color kinda changes a bit towards the bottom.
I think most people complaining about this issue (aside from those who have REALLY BAD yellow tinge) forget that these iMacs are otherwise great computers and there is no alternative in the Windows PCs for an iMac -- meaning a high-performance big screen computer that is super compact and stylish and has great functionality. Yes, the yellow tint issue is unaccaptable but it also is something that really counts only to those who demand absolutely perfect screens (graphics professionals). Now I could have replaced mine but I did not want to lose the best computer I've ever owned (yes, I mean even the quality of the display).
I would encourage you to go for it. If you get an iMac with a really bad yellow tinge, you can always replace it as Apple lets you do this. Hopefully you will get a perfect screen but if you don't and you get a screen that has a little bit of the yellow tinge... You have two choises: 1) either focus on the yellow tint tests or 2) actually use and be happy with your iMac.
Thanks Tigerman82 - thats exactly the type of feedback I was after. You've convinced me to get one I think