Somehow the Trevi Fountain manages to be more than the sum of its parts. I guess part of it is the magnitude, it is pretty sizable compared to most fountains, and the sculptures make it even more impressive. I hate to say it but I think the film "Three coins in a Fountain" has probably made this attraction what it is.
Nevertheless my mother marveled at it and she was delighted to have finally seen it. I guess the attraction of fountains is that the water moves and therefore the attraction is not static and can't be as easily captured on film as statues and monuments.

Very beautiful and very impressive day or night.
It does get busy though. Me and my wife got up at 4am and went. I'd recommend doing this. We were about the only people there but there is always police there too so it's not unsafe even at that time of night.

Trevi Fountain (Fontana di Trevi)
It a gorgeous fountain and is a must see if you are in Rome. Ignore all the cynical élites’ who say it not old enough to be considered an important Rome site. Modern cinema has made it a must stop for lovers of every age and the lovers were all around the Sunday my wife and I added our coins with a over the shoulder toss into the waters of this most beautiful Fontana. We will return to Rome soon.

Hi,
I live about 500 feet from the fountain, on Via del Lavatore.
When my family bought the apartment in the early 80s this was one of the most beautiful and romantic spots in Rome. Mass tourism combined with greedy shopkeepers and a careless local govenment have probably ruined the place forever.
All the roads that lead to the fountain are jammed with horrible restaurants (most of them don't even have a licence, so they can only microwave frozen pre-cooked meals) and souvenir shops that sell the same souvenir rubbish you can find in any European tourist spot: soccer shirts, ferrari models, various cheesy "art" pices, ugly clothes made in China.
Tourists (and denizens) are assaulted by all sorts of street vendors selling fake designer purses, toys, soap-bubble pistols, roses, noise-makers, etc.. From morning to late in the evening I hear gypsy musicians playing the same three songs (usually Guantanamera, O Sole Mio, the theme Godfather) and asking for coins at bars and restaurants.
Restaurants and bars spread out their tables to seat tourists in the middle of the relatively narrow cobbled streets (with foot and scooter traffic passing regularly), against any law or decency, because local police just don't care (or, worse, are offered bribes to look the other way).
Some eastern european mob has actually started importing kids with horrible phisical malformations to beg on these streets. You will see a kid with bent legs, strolling around sitting on a skateboard begging for spare change. It often feels like the center of calcutta, instead of a wealthy western city. As usual, local authorities just don't seem to care.
On the Trevi fountain square at least three "professional" statue-men perform all day (posing as strangely un-Italian figures such as the Sphinx and the Statue of Liberty), and three "regular" souvenir stands remind you where you are: in a tourist trap.(regular street vendors have a licence, and a stand, but they are likely to have obtained that licence bribing local public officials).
The coins you throw in the fountain are supposed to go to a local charity. Public officials (escorted by the Polizia Municipale, traffic police) turn up every morning, around 6.30, and collect the coins. But if you happen to drop by at 5.30 am, you will find a thug with a few henchmen, picking up bags of euros for themselves. This outragious robbery actually made the front page of italy's main newspaper about a year ago. For a few months it stopped, after which it continued its business as usual.

That said, the fountain is amazing and it's a must-see if you're in Rome. Just please please please follow this advice:

1) Visit the fountain between 6.30 and 9.30 am. You will love your visit, and get a feel of what this place used to be. Some days you might find the water not running (they turn it off to pick up the coins and for mantainance) but the peace and beauty is truely moving. And you can sit by the fountain and just wait for the show to start.
You can also go late at night (after midnight): you will be bothered by the street vendors, but they are harmless, just say no and - if necessary - tell them straightforward you want to be left in peace. Avoid other hours. The steets and the square are invaded by a croud of tour groups that will ruin your visit.

2) Don't give any money to any street vendors, performers, beggars, musicians. None whatsoever, no matter how sorry you feel for them, or how cute that fake gucci purse looks.

3) Avoid any of the restaurants in the area. Trust me: just stay away. You will be served rotten or overpriced food with terrible sevice. restaurants around here know there going to have a constant stream of customers and also know that it's very unlikely they will be back any time soon. So they only care about your money, not about you. Do yourself a favour, and stick to what your guidebook recommends in rome, don't just enter a random place you think looks good. The only place i would not miss is "San Crispino" for a gelato, a couple of blocks from the fountain (it's an institution, and it will definitly be in your guidebook).

4) Don't buy useless and cheap souvenirs. Souvenir shops have the magic power of transforming into a horrible tourist spot (just like any other major tourist spot in the world) what used to be a beautiful place. By buying their stuff, you are helping them destroy the place.

Thanks for going through all this. If you follow this advice, you won't make things better, but - maybe - you will not contribute to making them even worse.