This morning, I overheard two coworkers debating whether to use into or in to in the phrase "You are logged [into/in to] Flickr/Facebook/Picasa as ...". They ended up liking into in originally partially because it was shorter and they were trying to cut down on characters for that line.
I felt as though that in cases such as these, one choice is usually significantly more correct. A simple Google search yielded a Grammar Blog with an entry on into vs. in to. To steal from the blog: into is a preposition used often to indicate movement toward the inside of a place, in to is the adverb in followed by the preposition to.
I decided that in general I prefer in to when paired with the verb log in this context. So as the discussion continued, my other coworker and I butted in, both of us defending in to. But after a bit of debate, in end, into was used. I'm mildly disgruntled, but it's not my feature.
Logged in to means that you are logged in the manner in (as opposed to out) to a website, etc.. Logged into means that you are logged to a point of contact with a website, etc.. Both obviously work. I like in to because it has the parallel out of, which gives it greater specificity, and parallelism is nice in itself.
Here are some stats on the number of Google hits for various permutations of the phrases, since I thought they were interesting:
"logged into" 23M hits
"logged in to" 535M hits
"are logged into" 2M hits
"are logged in to" 46M hits
"log in to" 769M hits
"log into" 6M hits
Also thrown out there in the debate were login, log-in, and logged-in, just as points of consideration.
I'd be interested if anyone had thoughts on this.