Forgive me if this is an obvious question that everyone knows the answer to. But Rodney why do you prefer .PNG's? Aside from the obvious that they're decent quality but relatively small.
Back in the olden days before the PNG image format there was only one format that could effectively be used on websites that allowed images transparency. Nowadays most digital artists take this format for granted but many still don't realize the extent of it's utility nor how to take advantage of it.
Each image format has it's strengths and weaknesses but when dealing with web graphics PNGs are quite powerful. For instance, some people render or save to the PNG format but don't take the time to bother with it's ability to set areas of the image as transparent. And of course this is accomplished in A:M by rendering with Alpha Channels (i.e transparency) on.
I don't mean to distract you from more important work but... way back in 2008 I put cobbled together some random musing on this and related topics. PNG images were rendered out to formatted HTML which automatically organized and layered the output. I experimented with some of the basic options before getting distracted by something else that was new and shiny.
For a variety of reasons I termed the process
Lendering. Be careful, even three years later this stuff is still state o' the art.
These days formats such as flash/swf have produced pretty awesome stuff but... with the advent of HTML5 and other technologies who knows what could become of PNG art.
I'm not sure I answered your question... despite it's wondefull attributes PNG is probably not the best format for digital art. But it can do some things other formats cannot.