I don't get it. Okay, I get the idea of them. Apparently when you put a glass or a cup down on a table or something it's likely to leave a ring. I've gotta tell you though, I don't notice any rings on my surfaces. Probably because I have two young kids, and my surfaces are forever covered in yoghurt and crumbs, but still. I've never poured a drink that's so deliciously cool that it forms running condensation like in the adverts. I've spilled coffee sometimes, that makes a ring, but on no other occasion has this happened. Which leads me to the conclusion that coasters are exclusively for clean freaks and old shaky people.
Considering the ring-stopping nature of the coaster, I still fail to see the point. Surely it's just moving the ring to another venue? I feel like going to someone's place and saying "Eww, look at your dirty coasters." Besides, a coaster doesn't give too much protection against spillages. Sure, those old ugly straw ones can probably soak up a fair amount, but most coasters are non-absorbent, and only slightly larger than the cup or glass you're placing on it. Spill enough and you've just got a coaster shaped ring (square?) on your table. Back to square one, with a vengeance.
Okay, so let's say you're down with coasters. Which ones do you choose? There are so many. Different designs, different slogans, which coaster best reflects your amazing personality? Searching for coasters on Amazon via Google brings up several commemorative William & Kate royal wedding designs, and i'm pretty sure no one cares about that. But upon further research, there's a cornucopia of coaster delights. Floral, Mr. Men, sexy plain black in expensive materials, you can have anything. I got a bit excited for a second, until I realised that no matter what slogan or picture your coaster has, it will spend a large amount of time being covered with a beverage, and the rest of the time sitting there, not matching anything around it (unless you're really good at all that), and once the original novelty has worn off i'm sure everyone will think of you as "that guy with the lame coasters".
Screw that, I won't be that guy. My furniture will wear their rings proudly, and if anyone questions them, i'll pummel them to death with the coasters people have given me that are in a cupboard somewhere. "You want a coaster?! Here's your damn coaster! Embedded in your head, if you didn't understand my meaning due to your sudden onset brain damage."
Seriously, why would you want that in your house?