I didn`t try previous one, 1.5.0, but version 1.4.0 had some bugs, which seems to be corrected in the last one.
Adding WMS layers. There were some errors chosing more than one layer from server, but now it is repaired.
Ftools and defining Shapefile`s projection. Previously I got some python related errors, but from version 1.5.0 it works flawlesly.
Digitizing vectors gave headaches. If I have to digitize large area in large scale (or small scale.. which is more correctly?) - close enough, then i have to move base layer - it doesnt fit in screen. Moving layer is elementary - with mouse. But if I am digitizing in that time, how can it is possible to move layer? Dont have an extra mouse for layers... still i have shortcuts - keyboard arrows. This mouse thing WAS NOT working in v.1.5.0, so it IS working in v.1.6.0
I`m very proud that Grass support is almost fully implemented in QGIS. This gives huge additional boost for windows users. There`s no need to manually add qgis grass plugins, from v.1.5.0 it is included in one bundle. Install, next,next,finish and you get full qgis with grass support.