Anyone has any experience travelling on the sleeper class on the overnight train from Lisbon to Madrid? How long in advance do I have to do the booking in order to secure a place on the train?
Is it worth buying the railpass for Spain and Portugal?
Thanks in advance.

Have done it in Gran Classe (which is First with the private shower) and that was smooth, comfortable, and quiet. Food in the restaurant car was adequate but even not so great food can taste better as you roll along on a train sometimes. The berths are the typical size and the compartments are very compact.

Usually you can only book a max of 60 days out for this but it may have been extended to 90.

In terms of buying passes vs. point to point tickets definitely go to either www.railsaver.com or www.railpass.com and use the attached evaluation screens to make a decision about which option would be the most economical.

I travelled this route last year and booked a couchette the day before with out any problem.. if you are only travelling this route than it probably wouldn't be worth buying a eurail pass.. if you are going to travel throughout portugal and spain, and another country consider buying a eurorail select 3 country pass for as little as $304 if 2 people are travelling together. Go to ricksteves.com and review his eurail section to see if it would be worth buying a pass

Thanks Intrepid and hartwicks for the information.

@Intrepid : did you book the place well in advance? I shall have 2 days in Lisbon and am not sure whether I shall buy the tickets before I leave home or upon my arrival in Lisbon, I would also like to travel in the Gran Classe.
Thanks again.

I bought tickets well in advance but I was traveling during August which is probably a busier time. I had bought the tickets through RailEurope which, as you probably know, charges a premium, mainly for the convenience, as well as the shipping fee. I had a first class pass so I got a discount on the Gran Classe space.
I honestly don't know how to advise you but somehow I suspect you can probably wait until you get to Lisbon but if you do that I would make the reservations as soon as I got there.