When it comes to open source software, my most satisfactory experience has been with OpenOffice. Found here, this free software is an alternative to Microsoft Office and other commercial word-processing suites. For my purposes, which has mainly been word processing and some spreadsheet dabbling, OpenOffice is great. Additionally, I do all my browsing with Mozilla’s Firefox and I read all my pdfs with their Foxit reader. I switched to Firefox when they introduced tabbed browsing and for its general faster performance than Internet Explorer. I started to favor Foxit when Adobe Reader's Text-to-Speech started slowing down every file I loaded. (I think they changed this some time ago but old habits die hard.)
The only limitations of open source software is that it is the work of diehard volunteer programmers which makes updates and patches less predicable then the yearly releases from commercial software companies. Likewise, customer support really only exists in the form of questions posed on website message board which are,in turn, moderated by volunteers. I think the only major downside with open source software is that it requires designers to donate more of their time if they want software that remains current. OSS needs to be either a perfect standalone product (unlikely) or the fruit of collaborative and ongoing efforts.