I usually never buy back-ups of anything. By the time I have finished up a product, I already found something else I like.
However, I do have a back-up of both my brow- and eye pencil and I recently bought a back-up of both MAC Perfectly Pink and Young Spark lipglass. I also have a couple of back-ups of a lipstick and eyeshadow from "Manifesto" (from Isabella Rossellini) a brand that was sadly discontinued a couple of years ago
I agree with what people have said about always being able to find something new that you like. That coupled with the fact that it takes forever to finish a product. but i don't know how this applies to MSFs... I got into MAC around March 2007 through my friend who had 6 or 7 skinfinishes and it seemed like I waited forever (until July, lol) until I could buy my first. I have two backups of Global glow and a two humids just because I wanted one humid in my pan pallete and one in a pot
One backup of Guacamole eyeshadow, Viva Glam V Lipglass, Pink Clash Lipglass, Adventuresome Lipglass, Northern Lights MSF, #194 brush, Stud Eyebrows Pencil, and two backups of Roleplay Lipstick and Stereo Rose MSF.
I am starting to agree with my family, they say I'm "obsessed" with MAC
Oh well...................... Here are my backups.... I usually end up giving them away to friends or family. My cousin was just here visiting from England and I gave her 4 shadows
Summer Neutral (1)
Cosmic (1)
Firespot (1)
All Barbie shadows (1 of each)
Barbie Pearl Sunshine (1)
Shroom (1)
Brule (1)
UDPP (1)
Coco pigment (1)
Coppertime l/s (1)
Blonde on Blonde (1)
Barbie Rockin Chick (1)
MAC Barbie Dolls (2) saving them for the girls in the family
i've got a backup of mocha blush (i know it's not dc'd, but i found one at a CCO). i've also got backups of untitled and stillife paints and i guess i've got backups of elaborate and mad cap lipglasses (i accidentally bought extras of each cos i didn't realize i already had one until a few weeks ago...oops).
Edit: i almost forgot...i've got backups of silly, hi-resin rose, spin pink, and twirltone lipglass stains and a mini backup of restrained rust lipglass stain. i've also got backup of by jupiter and mercurial mineralize eyeshadows (mostly cos i wanted a different blend of the same shadow) annnnd i've got a backup of dig it eye khol (love that color...i should wear it more since i have 2) and violet-to-plum nail polish (same buying oops as above). whew! i'm really glad i have my cosmetic log done so that i can minimize my accidental dual purchases.
My first and only backup was purchased this month--Engaging! I love it, its like my staple daytime look with a bit of blitz and glitz fluidline. <3!!! I have Milady thats I guess tech. a backup b/c I'm not sure I want to crack it and use it.....
Aside from Brush Cleanser, the only backup I own is a BNIB Graphic Brown fluidline. In my humble opinion it is the BEST and MAC doesn't release enough new fluidlines in new collections for me to be comfortable just having the one I bought when A Muse first came out.
Don't Be Shy
Pearl Sunshine (2)
Shooting Star (I'm on number 3, I think I have 1 backup left in my drawer!)
Take a Hint Tendertone
Moth Brown
Stereo Rose
Young Spark l/g
Rainy Day n/p