The Career Doctor responds:
I strongly encourage all job-hunters to get the entire job offer in writing: salary benefits probationary period reviews etc. Having this information in writing protects both the employer and the potential employee.
I’ve known of a few job-seekers who never heard back from companies when they’ve asked for the offer in writing but my advice is always the same: you don’t want to work for a company that is not willing to put its offer in writing.
The only time I would recommend against asking for the offer in writing is when you are not yet at that stage in the negotiation.
For other tips and an overview of the process take a look at this section of Quintessential Careers: Salary and Job Offer Negotiation Tutorial.