Lemon Eucalyptus

I purchased a Lemon Eucalyptus from you a year ago. The plant is doing fine however it is approx 17 inches (40 centimeters) tall now and very spindly. Is this normal for this plant or should I be doing something to it to strengthen its stem.

Eucalyptus are high light plants and even seedlings require lots of light. This is hard to provide with natural light in temperate zones during the winter months. Keeping the plants a bit cooler will slow growth until good light returns in spring.
If the spaces between successive leaves has been increasing then the plant is not getting enough sun and is trying to get tall enough to reach more light. If this is the case you might want to move the plant to a window with more hours of sunlight or purchase a two light flourescent fixture to supplement the light for your plant.
If the plant does not seem to be "stretched" (etiolated) you could nip out the growing tip to encourage the tree to branch. You could shorten it to the point at which you wish branching to start as long as you leave at least 15 centimeter of stem with some leaves.