+1 - It is absolutely the best way of going from minor release to release.
The only time I have really run into problems with pkgbackup is when users are trying to migrate between major OS release, e.g. 3.2.2 to 4.3.1. That is a far more challenging scenario for any upgrade, never mind with a jailbreak on top.
gray_mouse, there have been a lot of updates recently, but it is not normally "every month". 4.2.1 was the place to be for several months before 4.3.x was released. There is rarely any reason to "rush" to the latest version. Usually much better to hold back a week or two, allow the jailbreak apps to be updated by their developers, and then take a decision...
I would be content on 4.3.1 for the time being... (I am!)