The basic formula in D&D Next for Spell Save DC is 8 + Magic Modifier + Proficiency.
However, the Spell Casting feature Paladins gain at level 2 says:
Magic Ability
Charisma is your magic ability for your paladin spells. The DC to resist one of your spells equals 8 + your Charisma modifier.
Do I get to add my proficiency bonus to this (like everything else)?
Yes.
As of Oct, 2013
Classes PDF page 42:
Spellcasting Bonus. If you present your holy symbol when you cast a spell, you can add your proficiency bonus to the spell’s saving throw DC. To present your holy symbol, you need to hold it, wear it visibly, or bear it emblazoned on your shield.
As of the Playtest Packet from September last year, no.
The proficiency bonus is only mentioned as a Spellcasting Bonus under 'Magic Ability' for Bards, Clerics, Druids, and Mages. Paladins and Rangers, (who only get access to spells later in their career), do not have it added on.
This is also specified in the 'Magic' section of the 'How To Play' document:
Saving Throws
Many spells specify that a target can make a saving throw to avoid some or all of a spell’s effects. The spell specifies the ability that the target uses for the save and what happens on a success or failure. The DC to resist one of your spells equals 10 + your magic ability modifier. If you have a spellcasting bonus from your class or another source, add the bonus to the DC.
(If someone has an updated version of the packet that corrects this, please mention it - it seems WoC took the packets down last year so I can't find a copy beyond what I used last year).
