We were reviewing some drafts of new user interface stuff at work today, and Colleague Tom noted that the title of one of the dialog boxes was listed as Setup Publishing. Momentarily unsure, he sent me a message: "Is setup considered a verb?"
Lots of people think so — search for "to setup" on Google, and you'll see page after page of results where people are using setup as a verb. You can do a similar exercise with "to login" and likewise find many, many instances of login as a verb.
Perhaps unusually, this is an instance where I actually do think that single-word spellings like these for phrasal verbs (as some of us learned to call them) are not sensible. Rather than simply calling them wrong, tho, let me justify this view with two pieces of evidence.
1. In many (not all) verbs like to set up and to log in, the prepositional bit (up, in) can move around in the sentence. Consider:
He needs to set up the computer.
He needs to set the computer up.
*He needs to setup the computer.
He needs to set it up.
*He needs to setup it.
The spelling in the marked (closed-up) examples doesn't represent the syntactical flexibility that's shown in the others.
For login, consider these:
She needs to log herself in.
*She needs to login herself.
Second one doesn't work, eh?
2. When you conjugate or otherwise do grammar-ish things to the verb, you do that only to the verb bit; the preposition bit is left unmolested. Consider:
I was setting up the computer.
I was setting the computer up.
*I was setupping the computer. (Thanks to Tom for that excellent example.)
Or even just these:
She sets up the computer.
*She setups the computer.
He logs in at the library.
*He logins at the library.
People will occasionally decide that a hyphen is just the thing -- to log-in, to set-up. This seems to acknowledge that the constituent parts of phrasal verbs are distinct. But in American usage, anyway, this is really no improvement.
I won't go into the detail about the technical definitions of a what constitutes a word (because I don't know enough about it, frankly), but it seems clear from these examples that when set up and log in are used as phrasal verbs (along with other examples, like sign up, write out, check in, and turn off), they're most logically spelled as two words.
As an aside, it's a general trend. Searching for one-word variations of phrasal verbs, I found these:
To reiterate, tho, I think that these one-word spellings are not the way to go.