Terrorism is a fact of life in most of the countries in the world, Nepal is just the same. At the moment there is much talk of a terrorist war but from experience the media may well be sensationalising a few stories at the expense of the image for a normally peaceful nation.
For a number of years there has been tension between the Maoist peoples and the King's government, not made any better by the occasional screw up on the part of the King when it comes to forging relationships with his people and continuing promises from the government about removing corruption.
This has led to a much publicised war between the two groups as the Maoists continue to fight for the right so sit around the government table.
In reality it shouldnt stop you from going to Nepal - The "bombs" that have been let off in the capital are little more than overgrown fireworks, their purpose is simply to demonstrate that the maoists have widespread support and are spread throughout teh country - their intentions stop short of deliberately killing people as this would damage support for their cause. Likewise they have made it clear that they will not target tourists or tourist sights as they appreciate how much tourists are essential to the country.
Recently the press ran a story of a mountaineering group being robbed by Maoists - this happened whilst I was in Gorkha - generally regarded as the home of the Maoists and the attitude there was that the Government was blaming every crime it could on the Maoist movement and the event was most likely just run of the mill criminals - the like you will find in any location where tourists flash very large quantities of cash about.
What you should be aware of though is the Bandhs - Nepali word for strike, when these hit it can bring all transport to a halt and many businesses might close up for the day. Likewise its not clever to be following demonstrating groups around - not that you'll likely find one anyway, but the police are poorly trained to deal with such things and localised trouble can erupt.
So for the ordinary tourist - relax, the chances of getting into trouble here are a lot lower than many other places in the world, follow the usual safety precautions that you would in big cities back home and keep an ear out for local advice and you'll have a great time.