Png has poor screen reader support, though it can be amended via an alt tag, I suppose. [ed: but breaks copy and paste, which might be bad for an about page listing address and contact information - personally I'd much prefer fallback font to a png].
It's a shame there are no "bandwidth" queries in css, like there are @media queries - the client should be able to say - just content and essential downloads, please.
It's a shame there are no "bandwidth" queries in css, like there are @media queries - the client should be able to say - just content and essential downloads, please.