I have heard beber and tomar used interchangeably as translations for the English "to drink." Is there any difference between the two, or are they exact synonyms when describing drinking a liquid? Are there regional differences in the use of these verbs?
I Spain, they are quite different, while "beber" can be used in a transitive or intransitive way, "tomar" can only be used as transitive for that meaning (I know that in America it can be used as a intransitive verb too but it is not used in that way in Spain). So you can say:
Estoy bebiendo un zumo.
Estoy tomando un zumo.
Estoy tomando. * (Incorrect in Spain, you need to specify what are you drinking: a name or a pronoun).
They can even used in a pronominal way when they are transitive:
Me estoy bebiendo un zumo.
Me estoy tomando un zumo.
As with "Beber" we can ommit what we are saying it often means that you are drinking alcoholic drinks, but it doesn't always mean that, it depends on the context, but if you use it in an intransitive way, people will likely understand that you're spaking about alcohol.
Si bebes, no conduzcas. (Here the context implies that we're referring to alcoholic drinks)
¿Qué estás bebiendo? (Here we don't know if it's alcoholic or not)
Bebe a menudo. (Probably we're talking about a problem with alcohol.)
So as with "tomar" we say what are we drinking, that confusion is not present.
In Mexico, at least, beber has a connotation of to drink alcoholic beverages, where as tomar is to drink anything (as well as to take, in other contexts).
The same sort phenomenon is observed in English in certain contexts...
Do you drink?
Is clearly meant to mean "Do you consume alcohol?" not "Do you drink anything?"
I have heard beber, or derivatives of it, used to mean non-alcoholic beverages. The "drinks" section of a menu is often called Bebidas, for instance, and may contain soft drinks, coffee, and tea.
In Argentina I never heard beber, it was always tomar. I could use the word beber but people would look at me a bit weirdly. (No references here, personal experience from living there)
Also if you wanted to ask someone if they drink alcohol, you would ask
Che boludo, ¿tomas? - Hey dude, do you drink (alcohol)?
When I learned Spanish a long time ago in school, they taught me that beber is more common in Spain but I don't have any references for that.
Random (possibly interesting) side note:
The yogurt I bought in a bag in Argentina is called "yogur bebible" and not "yogur tomable" =P
@Kage, in Spain we know someone comes from America when s/he says "tomar" instead of "beber" (in any context about drinking ;)
There is also, sometimes, the use of "beber" as "drink alcohol" when the drink is not specified.
"Tomar" is often used as "take", while "beber" is the most common verb used for "drink".