I’ve never used Magic Set Editor for the reason it was originally intended, I started using it to create Power cards for DnD 4e, originally using the (now removed) DnD 4e Universal Card Set, then modifying it to suit my needs, to redesigning the cards. One of the things I like about MSE is that you start with a base set of defined fields that have their values saved, and then you render those fields using a style, this meant that I could develop my card style using the same base fields and data as I had for the 4e UCS. I stopped using MSE when I stopped playing 4e, probably about a year ago when we started 5e playtests.
Recently we started playing Pathfinder Adventure Card Game and was inspired to start a project, from scratch, to create custom cards for the game. The process really helped get my head around how the MSE files are arranged and what you can (and can’t) do with the different object types. The process culminated in 3 styles – one each for Adventure Cards, Boons and Banes, and characters – which looked identical to the published cards.
At this stage I realised that despite Paizo’s fairly generous Community Use policy, exact reproductions of their cards would probably breach that policy. I didn’t have to start from scratch however, as I had all the field and data files from the previous incarnation, all I needed to do was tweak the style files. Recycling the code I had two design points in mind; the cards had to work with the published game (consistent colour-coding) and should stack (Adventure cards) or fan nicely (Name and Type on the card edges).
Version 1 is up on BoardGameGeek now.
Edit: After seeing this I’ve resurrected the original card styles.