Start by looking at the code directly.
National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 210 Branch Circuits
210.52 Dwelling Unit Receptacle Outlets.
(C) Countertops. In kitchens, pantries, breakfast rooms, dining rooms, and similar areas of dwelling units, receptacle outlets for countertop spaces shall be installed in accordance with 210.52(C)(1) through (C)(5).
(1) Wall Countertop Spaces. A receptacle outlet shall be installed at each wall countertop space that is 300 mm (12 in.) or wider. Receptacle outlets shall be installed so that no point along the wall line is more than 600 mm (24 in.) measured horizontally from a receptacle outlet in that space.
Exception: Receptacle outlets shall not be required on a
wall directly behind a range, counter-mounted cooking
unit, or sink in the installation described in Figure
So if you had a straight 28' countertop, with no sinks, ranges, fridges, etc. Then you'd need at least 7 receptacle outlets, if you wanted to be code compliant.
If, however, you do have sinks, ranges, refrigerators, etc. Then each bit of the countertop, will be considered its own separate countertop space.
(4) Separate Spaces. Countertop spaces separated by rangetops, refrigerators, or sinks shall be considered as separate countertop spaces in applying the requirements of 210.52(C)(1). If a range, counter-mounted cooking unit, or sink is installed in an island or peninsular countertop and the depth of the countertop behind the range, counter-mounted cooking unit, or sink is less than 300 mm (12 in.), the range, counter-mounted cooking unit, or sink shall be considered to divide the countertop space into two separate countertop spaces. Each separate countertop space shall comply with the applicable requirements in 210.52(C).
If you have a countertop space that's 4' or less, you'll only need one strategically placed receptacle. A countertop space between 4'1" to 8', you'll need two receptacles. 8'1" to 12' would require three receptacles, 12'1" to 16' needs four, and so on.