When answering the question "Why open source?", we are also inevitably faced with the question "Why not Microsoft?". This question cannot be answered both briefly and convincingly, which is probably the reason you were sent here. It's better to let the facts speak for themselves.
The following list of references was compiled mostly by skimming Slashdot stories from roughly the past two years, from June of 2000 to April of 2002. Undoubtedly I missed quite a few, but this should cover the more newsworthy items in the past couple of years. In many cases the stories have expired from their original locations, so only the Slashdot article is referenced.
The category names below represent my own subjective view of the stories; I encourage you to follow the links and form your own views.
Criminal Convictions
http://www.usdoj.gov/atr/cases/f4400/4469.htm
http://money.cnn.com/2000/06/07/technology/microsoft_ruling/
http://zdnet.com.com/2100-11-523518.html?legacy=zdnn
Lies and Deception
http://news.zdnet.co.uk/story/0,,t269-s2102244,00.html
http://seattletimes.nwsource.com/html/nationworld/134332634_microlob23.html
http://www.infoworld.com/articles/op/xml/01/03/05/010305opcringely.xml
http://www.infoworld.com/cgi-bin/displayStory.pl?99022.ecbombshell.htm
http://www.cantrip.org/nobugs.html
http://slashdot.org/article.pl?sid=02/04/10/1638207&mode=thread
http://www.microsoft.com/education/?id=DonatedComputers
Abuse of Monopoly Power
http://zdnet.com.com/2100-1104-868505.html
http://news.com.com/2100-1023-274980.html?legacy=cnet&tag=tp_pr
http://news.bbc.co.uk/hi/english/business/newsid_1590000/1590919.stm
http://news.bbc.co.uk/hi/english/business/newsid_1516000/1516753.stm
http://www.theregister.co.uk/content/4/20805.html
http://news.com.com/2100-1001-267992.html?legacy=cnet
http://news.com.com/2100-1001-257176.html?legacy=cnet&tag=tp_pr
http://news.bbc.co.uk/low/english/business/newsid_864000/864473.stm
http://www.computerworld.com/storyba/0,4125,NAV47_STO69389,00.html
Abuse of Customers
http://www.oregonlive.com/news/oregonian/steve_duin/index.ssf?/xml/story.ssf/html_standard.xsl?/base/all_wire_stories/101386428029222529.xml
http://wired.com/news/culture/0,1284,44906,00.html
http://www.wired.com/news/business/0,1367,41622,00.html
http://www.salon.com/tech/feature/2001/07/10/microsoft_school/index.html
http://www.usatoday.com/life/cyber/tech/cti739.htm
http://slashdot.org/article.pl?sid=01/07/07/1829241&mode=thread
http://www.aaxnet.com/news/M010425.html
http://www.internetweek.com/newslead01/lead032901.htm
http://slashdot.org/article.pl?sid=00/11/04/1437226&mode=thread
http://slashdot.org/article.pl?sid=00/12/01/0532206&mode=thread
http://slashdot.org/article.pl?sid=00/10/10/145245&mode=thread
http://zdnet.com.com/2100-11-524188.html?legacy=zdnn
http://www.kuro5hin.org/?op=displaystory&sid=2000/5/19/165146/255
http://www.infoworld.com/articles/op/xml/01/09/17/010917opfoster.xml?0920tham
http://www.zdnet.com/anchordesk/stories/story/0,10738,2779746,00.html
Invasion of Privacy
http://www.theregus.com/content/4/24611.html
http://slashdot.org/article.pl?sid=01/07/26/2159207&mode=thread
http://slashdot.org/article.pl?sid=02/02/20/2210256&mode=thread
http://www.infoworld.com/articles/op/xml/02/02/11/020211opfoster.xml
http://slashdot.org/article.pl?sid=01/04/03/1535244&mode=thread
http://slashdot.org/article.pl?sid=00/12/07/142200&mode=thread
http://www.joelonsoftware.com/articles/fog0000000047.html
Hostility towards Industry Standards and Open Source
http://opensource.org/halloween/
http://zdnet.com.com/2100-1105-845220.html
http://www.advogato.net/article/453.html
http://slashdot.org/article.pl?sid=02/03/17/2333207&mode=thread
http://slashdot.org/article.pl?sid=01/06/21/1810258&mode=thread
http://news.cnet.com/investor/news/newsitem/0-9900-1028-4825719-RHAT.html?tag=ltnc
http://slashdot.org/article.pl?sid=00/09/22/1333229&mode=thread
http://news.com.com/2100-1023-243144.html?legacy=cnet&tag=st.ne.1002.bgif.ni
http://www.webstandards.org/ie55.txt
http://news.com.com/2009-1001-215854.html?legacy=cnet
http://www.fourmilab.ch/webtools/demoroniser/
http://www.linuxworld.com/linuxworld/lw-2000-04/lw-04-vcontrol_3.html
Gaping Security Holes
http://www.usatoday.com/life/cyber/tech/2002/03/11/gilligan.htm
http://slashdot.org/article.pl?sid=02/02/14/000257&mode=thread
https://www.latimes.com/business/la-000003463jan14.story?coll=la-headlines-business-manual
http://www.eweek.com/article/0,3658,s%253D701%2526a%253D21023,00.asp
http://www.counterpane.com/crypto-gram-0201.html
http://slashdot.org/article.pl?sid=01/12/22/1329253&mode=thread
http://www.newsbytes.com/news/01/172878.html
http://slashdot.org/article.pl?sid=01/11/25/0616256&mode=thread
http://www.computerworld.com/storyba/0,4125,NAV47_STO64507,00.html
http://www.infoworld.com/articles/hn/xml/01/09/27/010927hnnimbda.xml?0927alert
http://www3.gartner.com/DisplayDocument?doc_cd=101034
http://www.newsbytes.com/news/01/170225.html
http://www.trusecure.com/html/tspub/hypeorhot/rxalerts/tsa01024_cid177.shtml
http://slashdot.org/article.pl?sid=01/08/20/2132207&mode=thread
http://www.eeye.com/html/Research/Advisories/AD20010501.html
http://slashdot.org/article.pl?sid=01/03/30/0413252
http://www.wired.com/news/technology/0,1282,42771,00.html
http://www.wired.com/news/technology/0,1282,42798,00.html
http://www.everything2.com/index.pl?node=MSTD
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-020.asp
http://www.theregister.co.uk/content/4/17679.html
http://www.sans.org/newlook/alerts/NTE-bank.htm
http://www.cnn.com/2000/TECH/computing/12/29/csis.microsoft.report.idg/index.html
http://www.infoworld.com/articles/hn/xml/00/11/03/001103hnhacker.xml
http://news.com.com/2100-1001-247716.html?legacy=cnet
http://slashdot.org/article.pl?sid=00/07/19/165251&mode=thread
Evading Justice
http://zdnet.com.com/2100-1104-835267.html
http://news.com.com/2010-1075-882846.html
http://news.bbc.co.uk/hi/english/business/newsid_1529000/1529036.stm
Ineptitude
http://news.com.com/2100-1001-872266.html
http://news.com.com/2100-1040-276911.html?legacy=cnet&tag=mn_hd
Other Lists
http://www.epic.org/privacy/consumer/microsoft/default.html
http://www.newbreedsoftware.com/bill/microsoft/
http://www.kmfms.com/whatsbad.html