step with a |O| tag is not showing at all. it's skipped and the next step is directly shown in the guide display window.

This is the correct behavior. Optional steps need to be given a condition, such as an item in the inventory or a previous quest completed. Otherwise they will not show up.

Ok fine, but then ther are optional step in old guides that are useless. Those quest for example saying "if you plan to do intance ABC, then take the optional quest".
Since ther is no possible condition.
This is not critical issue, but current guides need to be modified accordingly. Just tell me what you think, and I will remove those kind of steps when I come acroos one :)

cheers
iki

Yup, you can just remove the optional tag from them, but leave a note telling the user they can skip it if they want to. They can just manually click off the item if they don't want to do it.

I don't think the tag was well understood by a lot of the folks who were coding the old guides. I personally am not going to worry too much about the 1-60 guides atm, since they are going to get wiped out with Cata, but if you notice any mistakes in the 60-80 section we should definitely fix them :)