They're Just Not That Into You(r Manuscript)

I've written a children's book. About a year ago, I submitted my polished draft to publishing houses and agents. The book truly captures the child narrator's voice and experience, but it deals with difficult subject matter and I knew it might not be the most marketable thing ever. Still, I felt like every response, every rejection was a badge of honor.
I received a wide range of responses. Scrawled notes along the top of my manuscript copy, form letters, and even a real letter with a personal "I'm sorry, good luck." The ones that responded with personal acknowledgement thrilled me, as I felt like they were validating that the book was good, even if it wasn't for them.
Then, one day, the phone rang. I had been having a very bad week at work, so was a bit cranky at the unknown caller who mispronounced my name. My grouchiness dissipated when they told me that their small publishing house liked my story and thought it fit in with their other works. They were interested in my book! They didn't know exactly when they might be able to put out a new book, but they wanted me to know. Can I say it again? They were interested in my book!
I hung up the phone and did lots of happy dancing.
That was our only contact. No agreements were ever reached and I know it was just a preliminary call. But at what point can I send the book out again to a new round of publishing houses? Would it make sense to contact this publisher again and remind them that, at one point, they were interested in my book? Can I ask them if they still might be? Keep in mind, this was months ago. Perhaps I should have already contacted them for followup?
I was thrilled to hear of their interest, but would like to find someone who is interested enough to actually publish it, not just someone who will call me once and then leave me waiting indefinitely for some additional news or plans. I can get enough of that sort of thing in the dating world!

You can send it out to other publishing houses NOW. You're absolutely right to feel that this is not the most promising way to begin with a publishing house, so while it may yet work itself out at that small house, don't stop submitting.

You could remind this publisher of their interest, but months of silence tell another story. And what was that about not knowing exactly when they might be able to put out a new book? What, are they waiting for stock space to free up in their garage?

Submit, submit, submit.

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I submitted a book proposal to a publisher in June. They loved it and sent me a contract immediately, but then they decided they were not a large enough house to exploit the project as it should be. They suggested a larger house and a specific editor, and I sent the proposal package on to him with a cover letter telling him that the editor at the previous house had suggested sending it to him personally. That was in July 2008. I have heard nothing, even though the second publisher's web site says they respond in three months. Would it be rude/pushy to write to him and inquire? Would it be rude to submit it to other publishers? I don't know if they are actively considering it or it's sitting at the bottom of a slush pile.

It would not be rude or pushy to write and inquire. But you shouldn't necessarily expect an answer to your letter from the people who aren't responding to your submission.

It would also not be rude to KEEP SUBMITTING. Keep submitting.