Could someone tell me what the differences are between standard
Insert/update and WriteText UpdateText.

Say I have a table with one Text field and I want to insert a new record via
a strored proc that takes a an text parameter
Should I do:

Insert into Table(MyTextField, other Fields)
Or do
Insert into Table(other Fields)
select ID=Scope_Identity()
WriteText ....

I would have the same question for the Update.
As long as what is given to the stored proc is the new field, should I use a
Update, or UpdateText?

May be it does not matter.

I guess that since these operations are non-logged (in the case of simple
recovery model only?) they should be quicker to execute?
but not- rolled back?