I need to create a site that is very graphics-heavy (torn paper backgrounds with transparent shadows over textured graphics, etc.) One way that I was thinking of saving on file size was to drop all my background elements into one PNG. The issue is that this file is now 180k. If I break it up into various GIFs and a couple PNGs then it would be closer to 70k.
Does it really matter? What is "too large" these days for file size? Will anyone notice if the file is 180 or 70k?
If your users have fast access to your site (like, in an intranet), 180k is hardly a problem. If, on the other hand, the site is used by The Generic Older Person With A Humorously Slow Connection, it's probably going to be a problem. If your users use GPRS, but have endless patience, it's probably not going to be a problem. If the site gives out a million dollar to whoever has the patience to wait out the load time, transfer speeds are not an issue. And so on.
What I'm saying, it really depends on your requirements and constrains. This requires you to know (and subsequently tell us, for us to be more helpful) many things before you can get it close to right.
To avoid those pesky downvotes for very-valid-answers-but-simply-doesn't-please-someone, here's my answer:
180k divided by a standard ADSL modem transfer rate = 180kB / 100kB/s = 1.8s = endurable.