Some posts here are totally ridiculous. I had huge problems with the original install of Leopard, but didn't get on here to rant about it, I probably made some stupid little mistake myself that caused the problem. There is NOTHING WRONG with this security update. As a previous responder has stated, the person complaining should have adequate disk space before installing ANY update. Please stop bringing down Apple's rating on an update that HAS NO FLAWS.
How do I know that? I've installed it on three Macs. One has Tiger running, two have Leopard running, two are desktops, one is a laptop, two are G4 systems, one is a G5 system. All of them installed with no problem and the computers worked fine afterwards. They are large downloads, but do not take anywhere near half a day. I think all downloaded (separately) within a half hr or so. (Of course, this is with a cable modem, not a telephone line (dial up service).
Apple rocks, and, yes, we still have to play it smart ourselves & have backups etc. even though Apple is great, they cannot predict & prevent every possible condition known to man. Give them a break, and let's not hear such loud complaining, please!