Personally, When my users see Excel for Web (eg office365) if it looks like Excel then it must behave like Excel, and its MY fault not Telerik that it does not. They really dont appreciate that its Just Flipping Magic.
So just as you use the content menu to Insert a comment, the Comment is Resizable, once the comment is there in the cell you have the ref marker in the top RHS of the cell (a different css).
The text in that comment box would have reacted to Ctrl+B for bold, Ctrl+U for underline and Ctrl+I fir italic
Thats what my users expect.
Then also expect to cut and paste 'equally' between their own Excel Spreadsheets (which we are trying to wean them off of) and into the our online (CMS like) order processing system. They are very used to a sales order of 100s of line items (eg a WAN roll-out)  but the snag with your local bit of paper (excel file) is you have a version that is not 'controlled' (eg iso standards)  and you can have one hell of a problem in in billing reconciliation long after the job is completed because line items that dont match.  That is what your Excel spreadsheet control solves. What a comment achieves for a site item as an example, is whilst you gave the geotag telling you the location to install the WAN installing it in the basement is very different to installing it in the top floor of the towerblock or that you have to ring someone to get them to come out and give you access. So Cell annotation or comments is flipping useful and more over to be able scan your document for 'comments'.
Thats my feedback.

Yes of course. This feature could enrich all versions of Spreadsheet and Grid (AJAX, MVC, Core..)

Hi Rumen,

I'm considering whether to use a SpreadSheet control for a user interface where I need to present table data. Spreadsheet is not required but may be useful for its Excel-like handling. But I would prefer to have the opportunity to accompany to each cell a description of the data and one or more links to in-depth documents.