In my experiences both in-house and as a consultant/contractor I see many organizations letting people go that really should have stayed. The issue is that management didn't see the value in keeping that individual. As an IT resource you have to sell yourself every day--in good economic times as well as bad--to ensure management knows your value.
I've written about this a few times (http://daileymuse.com/2009/01/technical-jobs-in-a-downtrodden-economy/) and I always end up getting emails or comments from people saying "I didn't think of that." The problem is that we need to be thinking about this, and we need to think about it every day. An organization isn't going to shed a technical resource that is needed to keep the company in business. It is our job as that resource to show that we are a valuable asset that results in profitability.
It's also wise to put the time in to preparing your career in case you are affected by a layoff (http://daileymuse.com/2009/01/5-things-you-should-do-before-the-loss-of-your-it-job/). The worse possible time to work on your resume, references, etc. is AFTER you've been let go.
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