Xmarks (formerly foxmarks) is an add on for your browser that sycnronises your bookmarks across several machines. Sign up is free, and the add on works on internet explorer and safari as well as my beloved firefox (hence the change of name).
Upon adding something to my ever growing bookmark folder structure I click on the xmarks icon at the bottom right of the browser window. This sends my changes to a central server which acts as a master list.
Recently when I got a lovely iMac on my desk at work getting my bookmarks was as easy as visiting xmarks website and signing on. Within seconds all my favourites are available while also being safe in case of data loss at one of my machines.
The helpful people at Xmarks have also designed a site which displays my bookmarks on my iphone too, so I can have my bookmarks while on the move as well.
Altogether brilliant freeware, saving time and hassle as I work on 4 different macs, in OSX and bootcamp partitions in several different physical locations. (Its almost my current favourite piece of software …)