When it comes down to perceived web site performance for end users we're talking about how many bytes have to be transferred and how fast can they be transferred.

On the server end you're peered with the best OC-192 networks around so you're streaming bytes through chunnel sized fire hoses to, potentially, modem users trying to suck down bytes through a coffee stirring straw. 

It's this group of end users that could see potentially dramatic results by doing a few things you should probably already be doing in the first place.  Things like GZip Compression, which turns out to be surprisingly easy on IIS6.

With GZip compression you ought to be compressing your images to make them as tight as possible. Tools like PureJPEG or pngcrush can help you in this end.  It might even be a worthwhile metric at some point, especially if you're not posting images for reasons other than enhancing content, to make sure all your images are within some reasonable size metric, or that overall page size isn't beyond some threshold.  Because if you care about a 56.6k modem user and you're sending him a page with a couple 76k jpeg's on it, you're killing yourself and trying his patience.

Well pngcrush is *nix only.  Boo hoo.  Set up debian and run apache as just an image server, as you upload images to the server go ahead and process them with one or more of these tools.  Of course, some amount of post-inspection is necessary, while these tools are good they shouldn't be expected to verify their output is necessarily what you expect.

Link to PureJPEG through Dennis Forbes via Joel.

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