I think this is the closest dupe I've found so far for a MAC lipstick! They are pretty much identicle and the price difference is a good £10 which is a great saving!
The dupe I have found for Shy Girl is NYX Pumpkin Pie. I have loved NYX lipsticks ever since I bought my first one a few months ago and spotted this one on eBay the other week.
MAC Shy Girl is a peachy nude with golden shimmer and NYX Pumpkin Pie is the spitting image with the only different being a slightly more slippy, easier to apply formula and a purpley shimmer as opposed to a golden one. The different in the shimmer make the NYX lipstick ever so slightly pinker than Shy Girl but defnintely not enough difference to notice really, as you can tell from the photographs above.
So that my little dupe for Shy Girl! More dupes to come soon!