If you happen to have a lot of files in places that the installer would prefer you didn’t, notably /usr/local, then updating to Yosemite takes an unbelievably long time. Worst culprit is probably MacTeX — I’m pretty certain it would be a lot faster just to remove it altogether and then reinstall after updating the OS, but too late now.
On the plus side, the Yosemite installer seems to do a pretty good job of putting everything back in working order afterwards, which is more than can be said for most of its predecessors — in addition to LaTeX, all my Python, Fortran, Tk etc dev stuff seems to be working. Usually an OS upgrade means days of rebuilding. I’ll probably trip over a few things as we go along, but so far it’s looking surprisingly healthy.
Can’t all be good news, though, natch. As well as the frankly ugly new appearance and system font, there’s the woeful train wreck of Photos and the associated murder of Aperture. If you use the latter and haven’t upgraded to Yosemite, DON’T. The update that allowed the two to cooperate has been withdrawn from the App Store, so installing Yosemite is the end of the line*. If you’re not happy to be shepherded into the shitty new Photos app — and trust me, you aren’t — then it’s time to seek pastures new.
Adobe’s LightRoom is the obvious candidate, but I don’t like it and I don’t like them, so I’m currently checking out alternatives. Consequently, even though this has been Apple’s fuckup, it may finally nudge me to give Adobe the old heave-ho too. I’ve been stuck on CS3 for the best part of a decade, and that’s looking a bit rusty. I have no intention of buying into the Creative Cloud subscription model, and there seem to be a number of interesting new (or not so new) kids on the block, so let’s think of this as an opportunity.
Out with the old! (Present company excepted, obvs.)
* Update: although attempting to update fails, if you delete Aperture entirely you can – for the moment – re-download the app in its working form from your purchases. Don’t hang around, though, who knows how long that will remain the case.