What are some efficient ways to insert/change some amount of data in a web application for users that are used to do it in Excel sheets?
(the most efficient could be kind of subjective, and I would like to see several opinions)
I have found that for Excel-like applications, the best solution is simply to emulate Excel. So, to change a data cell for example, make any cell editable once clicked. To insert data, use the commands from an Insert menu.
The Google docs spreadsheet app has done an excellent job of making a web app behave in ways expected from users of it's desktop counterpart, and is a good place to look for examples and patterns you can emulate.