Hey all, not sure how this one got by me but I wanted to pop in and help out.
Sue, even if you took it from that site, your post was a huge help to LarryLasagne, thanks
LarryLasagne, I do not hear that tense often amongst the "general population" but your teacher is right in that using it is good practice.
The preterite continuous is used as Sue explained above and it is also important to note that there is another form of expressing the same meaning which is more commonly used in spoken Spanish (from my experience).
It is the use of the "pluscuamperfecto de indicativo" (don't mean to overwhelm you with this technical terminology) which in normal terms is a form of the helping verb "haber" + "estado" + the gerund form of the action verb.
For example, using Sue's examples above, I have added the alternative using the "pluscuamperfecto de indicativo" in parenthesis below the phrases...
Estuvimos bebiendo mucho aquel d�a.
� (Hab�amos estado bebiendo mucho aquel d�a)
I had been reading the whole morning
� (Hab�a estado leyendo toda la ma�ana)
Since the pluscuamperfecto de indicativo has a more standard structure (form of haber + estado + gerund of action verb), it is often easier for learners of Spanish to grasp and use than the preterite continuous and its often hard to use verb conjugations (irregulars and such

).
The two forms below are acceptable and will make you look like a pro

...
1) Estuvimos bebiendo mucho aquel d�a.
2) Hab�amos estado bebiendo mucho aquel d�a
True that it is best to learn both ways
Saludos & Suerte,
jer...