I created a simple notepad for personal use. It's a textbox that syncs to my server. I have a bookmark to it on my Kindle as well as a notepad widget on the new tab page of Chrome. It can also be accessed from my phone (any device with a browser, really).
When I'm on my computer, it's there every time I open my browser. Anywhere else, It's just a few clicks away.
That seems to be enough for me as I rarely need to sync files, and when I do, I have dropbox.
Edit: Also thought I should mention that before I created my own solution, I used Simplenote (http://simplenoteapp.com/) for the webapp and iOS app. Since then they've added an API and have a few other apps I think.
The JS checks to see if the contents of the textbox has changed, and if it has, it makes a POST request via AJAX to the server that saves it to a text file.
When I'm on my computer, it's there every time I open my browser. Anywhere else, It's just a few clicks away.
That seems to be enough for me as I rarely need to sync files, and when I do, I have dropbox.
Edit: Also thought I should mention that before I created my own solution, I used Simplenote (http://simplenoteapp.com/) for the webapp and iOS app. Since then they've added an API and have a few other apps I think.