They're fine as long as you don't want partial transparency.That's all .pngs do differently.
(
Mu Dinofiddler,
Fri 14 May 2010, 3:34,
archived)
but apparently .gif is evil because some company owns the rights rather than an open source .pngnot that i've ever known anyone to have legal issues using .gif or anything
(
gronkpan https://twitter.com/VomitingLarry,
Fri 14 May 2010, 4:02,
archived)