Is there ever a time when the word "onto" is separated into two words (ie. "on to")?

1) "“Onto” and “on to” are often interchangeable, but not always. Consider the effect created by wrongly using “onto” in the following sentence when “on to” is meant: “We’re having hors d’oeuvres in the garden, and for dinner moving onto the house.” If the “on” is part of an expression like “moving on” it can’t be shoved together with a “to” that just happens to follow it."
Source and further information:
http://www.wsu.edu/~brians/errors/onto.html


2) "Onto is the usual spelling of the compound preposition: He stepped onto the ice, lost his footing, and fell. As two words it may suggest slightly more independence for each of its parts: a combined verb (hung on) and a prepositional phrase (to his arm) in the sentence She hung on to his arm, for example. There is also a slang use of onto, meaning “alert to,” “aware of”: The police are onto this new confidence game."
Source and further information:
http://www.bartleby.com/68/91/4291.html


3) "ONTO vs. ON TO:
I. This pair works pretty much the same way the into/in to pair does, except that there are a number of sentences where either form would be correct, depending on the intended meaning. Take a look at some examples:
1. The responsibility fell onto his shoulders.
2. She tossed the book onto the desk.
3. We drove onto the turnpike. (We got on the turnpike.)
4. We drove on to the turnpike. (We drove until we got to the turnpike.
5. The restaurant adds the tip onto the bill.
6. Please pass this information on to your clients.
7. It would be more profitable to shift the cost onto your customers.
8. It would be more profitable to pass the cost on to your customers.

II. I actually believe that studying pairs #3 and #4 and #7 and #8 will tell you more about when to choose onto and when to choose on to than a lot of explanation involving grammatical terminology.

Just remember, the two expressions do not mean the same thing, so make sure you know exactly what you are trying to say, and then you will be likely to choose the right word or phrase."
Source and further information:
http://grammartips.homestead.com/into.html

What is on, to wit I know not what?

We changed planes in Chicago and went on to Baltimore.

This wouldn't ever have BEEN the word "onto," though. In this sentence, "on" is an adverb and "to" is a preposition.

Yup! For example, "Turn the light on to the second setting".

I think you may be on to something.

Yes, there is, and it has a different meaning too.

"Climbing onto the top of the ladder" would give an impression of achieving a goal, in other words attaining a particular position, either geographically or metaphorically. "Climbing on to the top of the ladder" would tend to emphasise the climb more. In other words it would describe a journey more than a destination.