I've done it before and it's especially nice if you've been roughing it a bit and are looking forward to a few luxuries like a comfy bed / good food and wine etc. Flying from Katmandhu to Schiphol pretty much guarantees you a lengthy stop at customs, though. Only time I've ever been searched.
Amsterdam's a pretty friendly place, I've found, so I wouldn't worry about being alone. Just find a nice looking bar and you'll find that people chat quite freely. Enough to do? Definitely. Even if the obvious attraction of the coffeeshops doesn't grab you, there's the Van Gogh museum which is pretty much my favourite art gallery in the world, Vondelpark for a nice stroll, a walk through the old bit of the city's always nice (Jordaan, all round there), loads of great restaurants (Indonesian ones, particularly). The red light district's good for a few wtf? moments. Etc etc. Mainly, though, its just a really beautiful city - very green as everyone's on bikes, hardly any cars in the middle, and a nice, slow pace if you want a relaxing weekend / lots of nightlife if you want the total opposite.