I started on Windows 3.1, and it was a good and stable product. At least, once it was set up right. I know my setup had problems because I was connected to a printer, and wanted a mainframe screen and a clock all running at the same time.

Then they introduced 3.11 "Windows for Workgroups", where they started getting them networked. I think that everything went downhill from that point onwards. NT, in it's early stages, was better - more reliable. But it was also very memory hungry. As nihil has pointed out, when memory was £100 for 8M, this was an issue - but give it the resources and it worked OK.

It seems that the more Windows has been expected to do, the more unstable it has become. This is probably because the basic OS model was not up to the demands that are currently put on it, but there is too much invested in the windows user base to change it.