Are the utilities worth buying?
The utilities are decent "fire and forget" properties, which pay for themselves quickly.  Think of them as equivalent to owning two railroads, but paying a bit better because you can't improve them further.  They don't have the same explosive-growth potential of railroads or properties, but they're cheaper.  You're not going to bankrupt anyone with them, but they can be decent money-makers over the course of the game.  They're better in the early game for fast and easy income, but later on they're more valuable simply as squares you can land safely on; everyone has become too rich to care much about such small rents.

A few comparisions:

Number of Utilities:


Cost $150, pays $28 (average roll of 7), pays for itself after ~6 rents.
Cost $300, pays $70 (average roll of 7), pays for itself after ~5 rents.


Number of Railroads:


Cost $200, pays $25, pays for itself after 8 rents.
Cost $400, pays $50, pays for itself after 8 rents.
Cost $600, pays $100, pays for itself after 6 rents.
Cost $800, pays $200, pays for itself after 4 rents.


Owning the light blue properties as a monopoly (much harder to get than just a utility or two!):


0 houses: Cost $320, pays ~13, pays for itself after ~24 rents.
1 house: Cost $470, pays ~$33, pays for itself after ~15 rents.
2 houses: Cost $620, pays ~$93, pays for itself after ~7 rents.
3 houses: Cost $770, pays ~$280, pays for itself after ~4 rents.


Edit: Someone has done a lot more math than I have: http://www.tkcs-collins.com/truman/monopoly/monopoly.shtml.