Bus from Santiago to Pucon/Temuco
 

There is a drastic price difference in taking a bus versus flight from Santiago to Pucon/Temuco in December 2009! Leaning towards bus but would like feedback please. Cama or premium service on overnight bus trip.........JAC vs Turbus?. Also, I don't think I can reserve/book bus trip from abroad...is this correct?

We did a similar trip by bus from Valparaiso to Pucon, stopping off for a couple of days in Talca. We used Turbus and I would highly recommend Cama as opposed to semi-cama particularly on an overnight trip. The Cama seats are extremely comfortable with wide seats that recline to 180 degrees and a reasonable food service. Semi -cama only recline part way and are narrower with less leg room. We used buses all over Chile, Argentina and Peru and much preferred them to the usually exhorbitantly priced airfares.

I'm not sure about booking from abroad as we were in SA for several months and booked as we travelled. However, Cama seats do get booked up early so unless you can book online or via an agent I would counsell booking seats as soon as you arrive in Chile (at any bus station) or maybe an agent can help?

You are correct, you cannot book from abroad. It is Premium seats which recline 180 degrees, Cama reclines 65. With Cama there are 3 seats across in a 2-1 configuration. Semi-cama have a 2-2 configuration. Premium seats are usually on the bottom deck of double decker buses with Cama upstairs.
http://www.turbus.cl/servicios.html
Turbus have offices in various parts of town or at their station on the Alameda at the Universidad de Santiago metro stop.
If your hotel is in the top eastern part of the city (Las Condes, Vitacura) you can get Turbus from next to the Vitacura municipality without having to go into town.
Buses in December can book quickly, so you would want to book as soon as you arrive. The evening snack is usually optional and we never get it but take our own snacks.

I am also interested in taking this bus trip.
I just checked out the website and although my Spanish is not great it does appear that you can purchase tickets electronically online.
Any comments ?
Alternatively does anyone know of Travel Agents who will pre purchase tickets for out of country customers ?

If you have a locally issued credit card you can purchase tickets online. If you have a foreign issued credit card you cannot.
I don't know of any travel agent who would just purchase bus tickets for you. Your hotel might.