Not really an issue unless the gauge goes through the roof!

As a suggestuion though, try flushing the rad, engine and heater matrix and refilling with a 50/50 mix of antifreeze and water.
When I changed the head gasket in my engine I ran the car on plain water for about a month, the temperature fluctuations were quite drastic but nothing to worry about.
As soon as I put antifreeze in (after flushing the engine etc..) the guage now happily sits in the middle of the range and only really decreases to about 1/4 when driving down the motorway.