Voted essential and have got more to add to the subject.
There is no need for the 'custom' text option.
We should be able to edit the dimension text itself by simply being able to write in the measured value box (although being able to edit the dimension text without a 'setting' box needing to be opened would be nice, as per the post http://archicad-talk.graphisoft.com/viewtopic.php?t=5692 ).
I previously used Drafix (2D only and cheap as chips, but more than adequate for documenting residential houses - as long as you can think in 3D while drawing in 2D)
Drafix uses the <> symbols in the dimension text to represent the 'measured value'.
After the <> symbols you can type in any custom text you like.
As you stretched the dimension the measured value changed.
If you delete the <> symbols then the dimension displayed only the text you had typed in.
If you had a dimension where the measured value symbols had been deleted, simply typing in <> at the start of the text reinserted the measured value.
A wonderfully simple way of managing the dimensions measured value and custom text.
Also, with ArchiCAD's dimensioning, the revert to default position should be on by default so the dimesion text is always centered within it's length.
Further to a dimension text capabilities of having an option for text under the dim line, when I was working in EU, I have come across with a standard that required special dims for openings - width of opening above the dim line, height of opening + sill dimension in brackets below. I have actually found that a very practical and tidy for preliminary dwgs which didn't yet have all openings resolved.
so it looked like something like this:
I just wonder how would you manage that with the current dim options.
The fact that you cannot add superscript without having the dimension becoming a 'custom' dimension is really annoying (not to mention dangerous when you are in a rush to finish a job), especially if many people are working on the same job at the same time.
I have gotten into the habit of changing the colour of the text so I know which ones are custom and which are not, but as you can imagine this is a slow process (not that I have to do it too often).
Can AC make independent the dimension and the superscript, and or, Make a custom dimension visually easy to recognise (ie so you do not have to select it to find out).
Please Graphisoft get the annotation field built into the dimension tool ASAP and make everybody happy. It is a relatively simple change, and the benefits for users in terms of saved man hours would be huge. Rudimentary Autocad has it.
A simpler and probably more practical solution (as stated before and aluded by others) is to just turn the dimension into an auto-text. That way it could be paired together with top/middle/bottom justification, and either use the "/" to feed the line, or else have it act as text with [return] to feed line. This way you could have text before, after, above, below, etc.