As I've gone through my life this has become clearer to me. Whilst you should be completely committed to serving your employer and their interests when employed by them you do need to look out for yourself. Every business should be focused on maximising its profit and developing the business. Part of that should be in developing its employees skills and abilities (I can, have and will write more on that subject). However, you cannot assume that you will always be employed by them. For a variety of reasons your paths may part. Then you will be in the market place again hoping that what you offer will be what another business wants. 

So my advice would be to actively and consciously :

• Identify the skills you are picking up in you current role;
• Seize opportunities to develop new knowledge and skills, training offered, stepping in to cover etc
• Make new contacts (social networks such as LinkedIn really help with this now), you never know when they might prove useful
• Collect recommendations when the work you have done is current - its hard to get them when the moment has passed
• Keep asking yourself "Am I OK with how I am personally developing at the moment?" If you are easy, have the courage to start asking yourself hard questions. Talk it over with good friends/family to get a perspective. What are your life goals? Is where you are going aligned with these. Try to remember that your career isn't everything. It is a large part of our lives but for most it is still a means to an end.