Should I post publications in preparation (or just submitted) on my CV? If I have works that are almost submitted to journals, or are in journal review, is it appropriate to include these on my CV?
Don't put anything in your CV you cannot justify if asked. A CV is not just a list of your accomplishments, it's a list of material you can provide to a recruiting committee in order to help them make a decision. 

In a same way that if you claim to have a given degree, you should be ready to provide the corresponding credentials, if you claim to you have a paper under review, you should be ready to provide the submission. 

In other words, you can list in your CV your submitted work, but not the pieces of work that are "almost submitted", unless you're ready to provide the draft if asked (the question is: if the draft is not submitted, that probably means it's not ready, therefore can you provide it?). If it's possible with the journal/conference policy, you can even put your submitted version on a pre-print site, such as arXiv. 

On going work can go into the "research statement" part of your CV, where you can explain the different ideas you're working on, and even give the key concepts.