title insurance will protect your client if the prooperty has been taken or allocated to be taken but didn't get picked up by the abstractor (although it would seem to me that someone, under those circumstances, forgot to tell the buyer their land was being taken), but it won't protect future takings decided on subsequently

That's correct it will protect against past happening but any future taking by the government.

After checking with our legal and state underwriting department, the question has been answered.  It is a case by case whereas the property can be taken (at a price) by the city or government for road expansion, development of land etc.  I found this link from expert law that was useful to my client.  Hopefully this will help others to understand eminent domain.  I wonder if one day, realtors will have to disclose this in a contract.  Buyers can never be promised this won't happen to them.  Pretty rare, but it does happen.  The Agent in my area  has already experienced this.  Here is the link to expertlaw.com

http://www.expertlaw.com/library/real_estate/eminent_domain.html

Thanks Charles and James for your comments and confirmations.