Yes, I believe that it is not legal anymore to deny coverage for pre-existing conditions, however do ask your new insurer about the fine print.  This rule may not be in effect if insurance is allowed to lapse for a certain period of time (i don't remember exactly how long this is, but believe it's somewhere between 30-90 days depending on the policy.)

For example, if you are changing insurance and there is a period of time between when you are covered by the old policy and when the new policy kicks in, you may no longer be protected by the "pre-exisiting" conditions clause.  This is especially important if your new company has a policy where an employee must be "on the books" for a certain period of time, before he/she is entitled to benefits.  If there is such a waiting period to receive new benefits, and the old insurance policy is canceled as of the last day of employment at the old company, you may find yourself being denied coverage.