From the Noteflight site:
“Noteflight, […] is dedicated to reinventing the way that people create, share and use written music. Our product doesn’t merely improve on other music notation software: it lets written music take advantage of the full power of the web as we know it today. Noteflight is a powerful full-featured application to edit, display and play back music notation in a standard web browser, integrated in an online library of musical scores that anyone can publish, link to, or embed.”
And from what I have experienced this is fairly accurate. It only took me a few moments to figure out exactly how it works. Start out clicking the measure you want to use and a ghost note appears. You then have the option to pick your value, eighth note or whole note etc. You can also pick your rests, sharps and anything else you need. All with the click of your mouse. Noteflight also has playback capability after you create your score. The sounds are all piano though, so don’t get too excited. Still, it’s a rather nice feature. Some how I missed the instrument choices. There are way more options than just piano. You can choose, bass, guitar, drums, violin, and different wind instruments. Sorry for my incompetence.
Screen capture of one of my attempts at scoring musical fusion.
You can choose to share your score or keep it private. You can also search using keywords or browse and see what you can find. Think Flickr, but with musical scores instead of pictures. There are other music sharing sites, such as iCompositions, though you must have instruments and the ability to record to participate. For Noteflight all one needs is a computer, which admittedly not everyone has, but you get my point.
Current issues include some keyboard shortcuts not working in Internet Explorer for Windows. Unfortunately these are the most used shortcuts: C (Copy), X (Cut), V (Paste), S (Save), Y (Redo) and Z (Undo). You may, however, use the mouse to perform these functions, so no biggie. An additional issue is that very large MusicXML compositions or MusicXML compositions with more than 20 parts may not import correctly. Two things about that. First, they are only on Beta version 3 and it should be an easy fix. Second, who the eff is doing more than 20 parts with this? Pretentious blowhards, that’s who (disclaimer: if you are one of these pretentious blowhards I am totally not referring to you, it’s some other pretentious blowhard). One other problem is that you are limited to using the volume on your computer only and mine is kinda quiet. I would like a volume option built in so I could boost it even louder. (insert obligatory Spinal Tap joke here)
I have actually been hoping for a program like this for some time. I can read a little music and have always wanted to be better at writing it to save the songs I create. Noteflight is a great way for me to ease back into it and get my knowledge level up. Where I think this program really excels,however, is in the experimentation. Even if you have no clue that there is this thing called music and that it can be the most beautiful or most ugly thing the world, sometimes both at once(I’m looking at you Frank Zappa), you can use Noteflight. Log on, create an account and just start clicking. Go there now and have some fun before they get wise and start charging for it.
TROZ
Some Kind Of Muffin 
do you have any songs to share?
Nothing worthwhile, yet