Let’s face it, you want to see Pompeii but quite frankly Naples is not a city you want to visit. Almost every traveler I have met on the road has told me just how unsafe they feel in downtown Naples: The cities lack of landfills has lead to complete stand stills of trash removal and when the locals incinerate it in the streets the gasses cause schools to shut down: The last time I was there I sat on a train in the train station for 2 hours (waiting for a 20 min ride) for what is still a mystery delay : I watched the police pull four teenagers and three dogs out of a train restroom (I have no idea how they fit in 
there or how they figured that was worth saving 15 Euro): and stray dogs and cats ruled the dry fountains and platforms in the train station. Still, you need a place to stay if you’re going to see the sights and I have the perfect suggestion.
The Fabric hostel on the outskirts of Naples in Portici not only gets you out of downtown (where you do not want to be) but is safe, very close to Pompeii and the Herculaneum, modern and great fun. Originally a textiles factory in 1860 this building was renovated into a modern hostel in recent years. The colors are vibrant and the dorm rooms are loft style. The bathrooms have an ultra chic feel to them with fogged shower windows (people can see your silhouette) and stainless steel sinks. There 
is a huge common room with a very nice sized satellite TV as well as plenty of seating and a refrigerator for storing your left over pizza; and speaking of pizza, Naples is famous for it and the hostel can direct you to some of the best you have ever had. The map below has the best and worst pizza places nearby. The better of the two on Corso Umbertol has a discounted price for anyone staying at the Fabric which comes to about 4 Euro for a marghertia pizza cooked right in front of you as you wait with the owners.
Around the corner from the front desk which is open 24 hours at the hoste
l is a large room complete with bar and stage. Although there were no performances when I was checked in, there apparently are nights during which this area turns into a disco of sorts. Even on more relaxing nights this is a great place to mingle with other travelers over a drink. One short coming is a lack of usable kitchen but this is made up for by the inexpensive pizzerias mentioned above and the snacks available for purchase at the bar. If you still need something else there are a couple grocery stores right down the street (towards the plaza) where you can find anythin
g you need for sandwiches or quick snacks.
In all I never felt unsafe in Portici and the hostel brags that it is located in one of the only parts of Naples that has trash pick up still. Following the directions on the website lead to a lot of confusion in finding the hostel for me and as I see from other reviews, other travelers as well. It just so happened that I went the completely opposite direction and followed the coast for about 3/4 of a mile until I gave up and tried conversing with a local shop owner. After some broken Italian and a lot of hand gestures the Italian gentleman said “Aaahhhh, big new hotel!” Turns out the place is fairly well known. Study the map below and get your bearings when you come out of the Portici-Ercolano train station. Heading straight out of the train station as the hostel suggests is a bit of misdirection. Look for Corso Umbertol which is the street lined with trees (and doesn’t follow the coast).
Once you are there and settled in the staff will be very helpful in answering all your questions. There are train time tables and maps on the walls around the check in desk and everyone speaks better English than you probably do Italian. Getting to the train station towards Pompeii is simple and easy too. Just head directly up Via Liberta (green line on map below). When I was there (May 07), there was some construction going on at the station which made it difficult to figure out which side of the tracks to catch the train. This may be fixed now but in any case you want to go to the opposite side of the ticket office (north side).
A visit to Pompeii is definitely worth it if you have time after Rome, Florence and Venice. Feeling safe and being in a great location at a great 
price (around 25 US dollars even in the high season) makes a visit to Naples not only memorable for all the right reasons but logical. It is wonderful that the Fabric hostel can provide all it does for travelers who might otherwise be intimidated by all the Naples horror stories they hear on the road. If the opportunity comes up, don’t worry, head to Portici and book a room at the Fabric Hostel.
Going anywhere near Naples without visiting the wild city is like going to a tropical island and being afraid to go anywhere near the water. You’re simply missing on a very special and different experience. Sure, it may be filthy, stinky, filled with crime, racing cars everywhere. But underneath is the life of warm people who know how to enjoy life. Go around, have a pizza, go at night to the piazzas and have beer with the locals as some street jazz band is playing for money.
Getting on and off tourists buses to visit the “must see” sites like pompeii, make a few camera clicks and go on is something you can do when you’re 80.
Great point Uri! If one feels up to it I would suggest whole heartedly to engage the culture on their own turf…no matter how stinky the city is…just take precautions against the crime.