Playmats are one of those things in Magic, along with deck choices, that can really allow players to express their magical "identity." You see it in cards with casual players and their Johnny combos, you see it with competitive players and their choice of aggro or control, you see it with me and Merfolk.
It also comes out in playmats. Obviously I have a hand-painted Silvergill Adept as my playmat, and it's amazing. I also people with events from their favorite Grand Prix or custom-drawn with their favorite art.
And in case you're looking for a touch of Planeswalker-related humor, here's one for you.
I saw this posted online today, and I thought this picture alone was worth sharing because of how awesome it is. Poor Tibalt always gets left out. The high-res image is located here.