HI greyfox
We have also been updating for quite a while now, but personally I would always update a staging-system first (or create a local setup as similar as possible to the production system, clone everything in there, and then run the update). You can expect a few breaking changes in 5.4 as in every version, especially if you are using a custom skin (e.g. comming with the new customizable menu and some changes in the hooks there) and I would suspect that there will be more need for adapations for 6.0 (especially if you are not running a run of the mill system, i.e. you maybe have a few patches and special extensions). The plugins need to work with the new version, sometimes this requires an update bigger than just changing the compatibility in plugin.php. The update process sometimes asks you to take decisions, so it is easier if you are prepared for them :-).
But in general, once all your local idiosynchrasies are sorted out, the update process is rather painless. The usual warnings apply (make a backup of the database and now how to get your webroot back to its previous state).
We have also been updating for quite a while now, but personally I would always update a staging-system first (or create a local setup as similar as possible to the production system, clone everything in there, and then run the update). You can expect a few breaking changes in 5.4 as in every version, especially if you are using a custom skin (e.g. comming with the new customizable menu and some changes in the hooks there) and I would suspect that there will be more need for adapations for 6.0 (especially if you are not running a run of the mill system, i.e. you maybe have a few patches and special extensions). The plugins need to work with the new version, sometimes this requires an update bigger than just changing the compatibility in plugin.php. The update process sometimes asks you to take decisions, so it is easier if you are prepared for them :-).
But in general, once all your local idiosynchrasies are sorted out, the update process is rather painless. The usual warnings apply (make a backup of the database and now how to get your webroot back to its previous state).