ScribTeX helped me a lot a few years back when I had a conference paper due in a couple of days and only an old PowerPC machine at my disposal at home that had trouble running MacTeX (for reasons I had no time to fix). I ended up writing most of it in the browser. Then the killer feature of ScribTeX for me was that it didn't require registration; you could use it from anywhere right away if you had your TeX files with you on a flash drive. It wasn't that registering or logging in was hard, mind you, but not having to do it completely bypassed the mental barrier of entering your password in a potentially unsafe environment like a malware-infested university computer lab. Later you would be at a safer computer (e.g., your own), log in to ScribTeX and upload your document to it as an off-site backup.
ScribTeX helped me a lot a few years back when I had a conference paper due in a couple of days and only an old PowerPC machine at my disposal at home that had trouble running MacTeX (for reasons I had no time to fix). I ended up writing most of it in the browser. Then the killer feature of ScribTeX for me was that it didn't require registration; you could use it from anywhere right away if you had your TeX files with you on a flash drive. It wasn't that registering or logging in was hard, mind you, but not having to do it completely bypassed the mental barrier of entering your password in a potentially unsafe environment like a malware-infested university computer lab. Later you would be at a safer computer (e.g., your own), log in to ScribTeX and upload your document to it as an off-site backup.