There will always be a newer version available. It makes sense to use the latest stable version there is at the time. Today this is version 7.0. One of the release date suggestions for the version after 7.0 was March this year! You shouldn't wait for anything.

When upgrading - if you have paid for the OpenERP Enterprise platform, then your database is migrated to any new version by OpenERP support. This migrates all configurations, and all data imported into and/or entered into the software. If you have not paid for this, you are on your own and must migrate your own database and/or data.

Any custom modules (programming) need to be upgraded either by yourself, or by someone else. OpenERP can do this for a fee based on the number of lines, many partners can also help. The major changes from version 6.1 to 7.0 included things related to the data model (mainly res.partner) and the syntax for views (some XML). Any modules that were affected needed to be edited (or re-written, depending on their complexity).

You can presume all you want about what will be available with the next version, I would never recommend using anything not released.