It's silly really - but I love being able to do my annual report on utilities because i've been tracking it for so long, I am able to create pretty graphs. Keep in mind that each month is that which the utilities were billed, so if it was billed in November, it was actually the utilities used in October.
The trend line, while a bit bumpy, cleary shows the dip one would expect to see in the summer - and spikes in colder months.
For those that find the above graph a bit too cluttered, this one shows the monthly average a bit more clearly - I use this data to predict my monthly bills now for budgeting purposes and find that I'm usually within about $10! I'de say that's worth doing all this tracking.
The last little graph I have for you is the combined monthly average year over year. Remember that we've only been in our current house for the last two years - and the differences was less than $2.