(first of all: great software – not perfect, but hey, it’s a beta and I really like what I see so far, I’m definitely gonna use XF instead of vB in the future)
I understand you probably use JPEG for file size reason, but this creates problems with (alpha)transparent PNGs. Having support for real transparency is important for my forum, as we have several styles with different background colors, so always replacing transparency by white is not really an option.
Can’t you just use the format the avatar was uploaded in for the resized versions? I modified my test forum to do that and my avatar (the same one I use here, it’s a PNG) keeps its transparency (and also, the border looks better). Or at least make it an option which format is used. This is a much bigger issue to us than disk space or traffic.