Recently, I feel like fewer people are thanking PUG participants for coming to their group. If things progressed well, and a random player pulled his/her weight while staying with your group for hours, offering a simple “Thanks for coming!” or some kind of acknowledgement goes a long way. Even if they aren’t the best performer, they are spending hours of their time with you, so you can still say thanks.
Do PUG participants deserve it? Well, I suppose no one is owed anything. But, if you need an extra healer/tank/DPS to be able to raid that night, and you risk not being able to raid at all without that extra body, a quick thanks feels good. This is especially true with progression. If a PUG sticks around with you for a long time even though the boss still stands at the end of the night, give them a high five before signing off.
Just simple things like that can make things a little nicer on Azeroth