A while back, the Gaim chat program got renamed to Pidgin for complicated reasons. Fedora duly released a pidgin package that said it replaced the old gaim package, and I duly typed yum update on my x86_64 machine, and things came to a screeching halt with errors about file conflicts. It turned out that the updates repository had both the i386 and the x86_64 versions of pidgin, and yum was picking the i386 version, which depended on various i386 packages that conflict with the x86_64 RPMs that I already had.

One reason that this could happen comes down to package naming. Namely, Fedora made the decision not to burn the package's architecture into the package name itself (unlike in the Debian world, where there would have been pidgin and pidgin-i386 packages). This meant that both versions of pidgin could assert that they replaced gaim, as opposed to something like 'pidgin-i386 replaces gaim-i386' for the lesser architecture.

In turn this is pretty much necessary to keep package naming sensible and not make a bunch of extra work as you migrate and not have packages that only differ in name. Otherwise, a native i386 only machine would have 'pidgin', but the exact same bits would be called 'pidgin-i386' on a multi-architecture machine.

(The way around this sort of issue is something like yum update pidgin.x86_64; this gets yum to pick the right version as the update.)