As a small business owner, should I be concerned about a tax lien?

Only if you have either not paid or defaulted on your tax obligations from the State, City or Federal Governments

Yes. Like any lien they affect your credit rating and ability to borrow. With some exceptions IRS is in first position for debt to payment. 

question is too general 

if you owe money and dont pay with time you can get a tax lien however you will receive notice before it happens

You should ALWAYS be concerned about a tax lien whether you're in business or not. Having any type of lien against you will be a real handicap should you want to finance a home, business or whatever. Avoid liens at all cost. You don't want them showing up on your credit report!

As others has stated tax lien is on real properties  or stock which is earning interest.  You owned a hotel and get behind in your taxes, then the IRS will place a lien on your hotel.

Yes. They can start levying income and/or your bank accounts. 

Yes, it will hamper your ability to get credit 

Yes, you should be concerned.