Brent Simmons raises a question as to when developers (of currently Universal Binaries) will drop PPC support.

Disregarding technical forces and business reasons, I think the best time to drop PPC support is when Apple does. MacRumors/AppleInsider posits this will be with OS X 10.6. Then you know that anyone still with a PowerPC machines isn't running the latest and greatest anyway, and is probably "fine" with no updating to the current version of your app ("This machine is stuck in 2007, which is fine with me for now") they might say.

At least, for single-user applications. Client/Server apps will probably need to support PPC for much longer, to give time for all the machines in a facility time to be replaced with Intel ones. As a business myself I try to keep my machines around for at least 4-5 years (depending on financial situations, when I last bought a machine, and if I'm forced to upgrade for a project like buying the first Intel iMac for Univeral Binary work). So, if you extrapolate that, people will be using PowerPC machines at least until 2012 in office situations. So call it at least until 2015 when client/server apps can end their PPC support/support for "that old version of the client". 2017 if you want to give people a full decade to migrate (which might be excessive).

Maybe it's because I'm that way though: I expect anything I pay $3 for to last me the rest of my life, or pay for itself at least 50 to 100 times over. ($3, because obviously anything you pay $1 for will break in a week). I've had more people in the last month say "Oh wow, that's an old machine", when I mention I'm on my first gen Intel iMac. Me? I'm hardly halfway through the life of that machine!!