The commented cells in Excel 2010 by default will only show a marking next to them indicating that there is a comment for that specific cell. Only on hovering to that marker will a comment pop up.
However, this can be changed so that comments are prominently visible for such cells.
To do this :
Go to File > Options.
Next, in the Advanced column, scroll down to the right side section “For cells with comments, show:” and change the option from “Indicators only, and comments on hover” to “Comments and indicators”.
All done. From now on, all the commented cells will display both of these visibly for all spreadsheets.