Hope this clears up some misconceptions people are having.
The old reason at least for the M$ thing was because the company was built moreso around businessmen than engineers and developers. This is still true to some point, Ballmer himself has a Harvard business degree rather than computer science or some such related.
MS were also the real contributers to the "make the hardware free (as in free to be whatever you want) and pay for the software". This is what gave them the edge over Apple, a predominately "Hardware" based company, selling whole, steady computers, designed to not need to be altered. With this in mind however they need to sell their software at heavy prices and have always had pretty crummy ways of wrapping around companies and forcing them to upgrade software, such as a MS Word 2007 file not working with a Word 2004 copy, Windows XP server accounts not working with Windows 7 or selling different versions of their OS such as Home Premium/ Office etc., charging nearly double for one or two key differences.
MS work around making the old incompatible with the new and charge stupid amounts for an upgrade, hoping for a wave effect across companies who'd need to upgrade 100 or so computers.
This gets them a bad enough rep, but what's causing them to grow really old in the tooth is their hostile attacks on services like Linux, a completely free OS, and Google, who sell their software for free, with the intent to get money of the users through ads later from using the internet. A good example being OpenOffice, a freeware Word alternate that can read and create .doc files and can do many of the things Word can, but has been stamped out of major public eye by MS wanting to earn a profit on their product.
Many computer users then would argue that MS have such then been throttling the continuing development of computers, business and personal, by using low and dirty tactics and developing their monopoly on computers around the world. Rather than trying to creating "the best product" and charging high prices for such, like what Apple does, they get charge a small price for the computer and then trap people and companies into a cycle which is difficult to break free from and also very expensive to continue on.
The only real place where they've done good in are in the games development, primarily because other developers (like Apple) turned up their nose at such mediums, but even then their programming languages are among the most archaic and ill-developed, only holding onto them because it was their standard back when originally developed.
In a final bit:
MS are no worse than Coke or McDonalds *as a business*, but the market for computers has changed so dramatically over the past two decades that many would agree we need to move on in certain fields. This is something that requires brains, not just money, and while Google and Apple are continuing on their own, MS' resilience to letting go of their archaic monopoly is what most would argue is stunting the growth of computers as a whole.
Hense the why people tend to refer to them as M$.