I personally think that there should be some plugins that can easily be integrated into themes, whereas there are others that should be only used as plugins.

For instance, a redirect to a Feedburner Feed is something that I think should be built into the theme rather than have a separate plugin.

I think it really depends upon how many additives there will be. If it is simply a redirect, then by all means include it in the theme, but when it adds a feature like voting or something, then I think it should be a dedicated plugin, mainly because not everyone will want the voting feature, where the majority of people would prefer a redirect to Feedburner.