I'd say its in transition on the whole, but especially in IT. Massive companies like Sony, Toyota, Nissan, etc. still have a lifetime employment structure, but once you get hired to any company here, it's still real hard to get fired.
Answering your question would really take a small essay because the answer is yes and no for SO many reasons.
EDIT: I think I misread your question the first time. It can be difficult mostly because firms here are used to having employees who are generalists, work in every part of the company through the years, and become upper management who have a much needed knowledge of the whole company. In the west in general, we focus on one area and change companies to grow our skills in that field. This is a problem because its really hard to change companies in Japan and Japanese employers often want you to learn new skills to work in different areas of the company. In short, it's difficult to become a specialist in Japan without sacrifice (usually salary). But there are many new technology companies that are trying to change that pattern.