I don't buy a bag just because someone else has it, but I have fallen in love with bags after seeing how awesome they look on someone else.
Same here! Seeing someone carrying the bag IRL, seeing how they use it, how easy or hard it is to get into and out of the bag when also toting shopping bags, holding a child's hand, or just going about their business. Looking at how the bag has transformed itself over time as the leather has broken in a bit. This can make me fall in love with a bag I never wanted before.
I saw someone at the outlet carrying a plum (?) Maggie, not the embossed one but the regular leather one. I'm not a Maggie fan but I loved the way that plum Maggie looked, and I actually thought I might pick one up if I could find one in that color.
This has happened with siggy bags as well. One of my coworkers has the orange/magenta Glam tote that dawnqueenb69's DD has, and it just looks so summery and cheerful which is a boon for schlepping to work. I was drawn to this bag when it was in the outlets but not enough to buy it at the time, but this was when they were still only 30% off.
I saw a lady carrying a beautiful black/black siggy Carly earlier. The bag was giant, plus the lady was petite, but it looked fabulous on her! I missed the Carly craze and I much prefer Zoe and Brooke to Carly, but I enjoyed seeing this bag in action and I have a new appreciation for Carly.
OTOH, seeing bags carried IRL has turned me off of them, too. I saw someone in line fishing through their well-stuffed siggy Peyton carryall once, and I thought the bag looked awful (sorry to those who might have and love this bag). It just didn't look right stuffed up and hanging open on a shoulder. This was not long after I'd purchased a leather Peyton carryall but was unsure about keeping her because of the open top. I eventually returned that bag, mostly because of the open top but seeing it in action on others didn't help.