Of course, working with a Linux desktop eventually requires you to work with an office suite. Although I have used alternatives like AbiWord and Calligra in the past, and although I do think that Google Docs might eventually become powerful enough to use instead, I’m currently using LibreOffice.
The use of LibreOffice for Linux users is well known: it has decent Microsoft Office support (although I hardly ever need it; most users don’t mind exporting the files in an open document format and publishers often support OpenOffice/LibreOffice formats themselves) and its features are becoming more and more powerful, such as the CMIS support (for online collaboration through content management systems). It also has a huge community, sharing templates and other documents that make life with LibreOffice even much prettier. Don’t forget to check out its extensive documentation.
The aspects of LibreOffice I use the most are of course its writer (word processor) and calc (spreadsheet application). The writer-part is for when I do technical writing, whereas the spreadsheet application is for generating simple management sheets for startups and households that want to keep track of things (such as budgets, creating invoices, data for mail-merge, etc.). At my work, Excel is one of the most used “end user computing” tools, so I happen to get acquainted with quite a few spreadsheet tips and tricks that are beneficial for small companies or organizations ;-) Also, Calc has support for macro-like enhancements, which makes it a good start for fast application development (until the requests of the user/client has been stabilized, after which I usually suggest a real application development ;-)
I generally don’t use its presentation part much though – if I get a powerpoint, I first see if Google Docs doesn’t show it sufficiently well. If not, then I try it out in LibreOffice. But usually, if someone sends me a presentation, I tend to ask for a PDF version.