I heard of the site. Do you have any experience with it, or heard some details on safety and effectiveness?
I'm using it for day-to-day work. It's no more likely to catch a virus than MS Office is, and I can type letters in one just as fast as in the other. Spreadsheets, too, are limited only by my ability to write them correctly. But in fairness, programmers who have written extensive Basic scripts for those spreadsheets report that Open Office scripts slow down somewhat earlier than Microsoft Office scripts.
When someone sends me an attachment in "Word," will I be able to open it using the site's program?
Basically yes. I'm hedging a bit because documents with lots of macros might run into portability problems. But your typical letter, business memo, masters thesis etc will work just fine.