There are two things every content writer knows:
1. Spreadsheets suck
2. The bigger the website, the more sucky spreadsheets get
My advice is to never use spreadsheets for writing content. Content goes in the design, so you should develop it in the design. This, obviously, becomes impractical when you are not the person who is designing. (Although I hope you are working very closely with the designer.)
Nonetheless, you should at least be able to develop content directly on top of the design. After some digging, I found a relatively simple, free way to do this. I would like to share it with you in the hope that if we ever work together, there will be no spreadsheets used for content.
Whatever it is that needs content, save it as a PDF.
Open the PDF in Preview.
Go to Tools > Annotate > Add Note
Click precisely on the spot you need to write for. A window will open on the side.
Type in your content.
As long as the designer opens it in Preview, she will be able to copy and paste your content into the design, without having to deal with a spreadsheet.
In conclusion, please for the love of god stop using spreadsheets for content development.
Oh, and if you know of a better/prettier/non-mac-only way of doing this on top of any design, on or off-line, for free, please share. Pretty please.
UPDATE 3/25/10: Notable is even better.