Bug 158556 is "Manual hiding of panel." In KDE 3, you could manually hide the panel at the bottom of the screen. In KDE 4, you can't. KDE 4 offers an "auto-hide" feature, where the panel will randomly pop up and down in an attention-stealing way based on mouse position. There is no longer any way to hide the panel manually.
The official position is that you should use auto-hide instead of manual hiding, and the relevant maintainers have been consistently insulting to users who complain about it. The bug (which is a regression - it worked before and then was changed so that it doesn't work anymore) is misclassified as a "wish list" item. First reported in February 2008: almost three years ago. It is currently the fourth highest-voted item for its module ("plasma") on the "Most wanted features" list; it has also received more votes than any item for its module on the "Most hated bugs" list, and so would top that list if it were properly classified.
Bug 180051 is "Need a way to have default printer settings." When you attempt to print a document, the print dialogue offers two buttons for configuration, either of which can be expanded to show selectable options. One of these controls the CUPS options, set by the system-wide print server. The other controls the Qt options, which are local to Qt (in practice, local to KDE). The Qt options override the CUPS options; and every time the dialogue pops up they are reset to Qt's hardcoded defaults. The usual way this manifests in practice is that users who want duplex printing will set it up in CUPS's system-wide defaults, and then be surprised that KDE applications consistently print in simplex. More sophisticated users will dig into the "Advanced" options in the print dialogue, see that their desired settings are correctly reflected there, and be even more confused. A few users figure out that they can set duplex printing in the other options section, but are frustrated by the fact that they must do this on every single print job. On some systems, there's a similar issue between A4 and letter-size paper. Affected installations, especially in multi-user environments, typically end up with a number of printer stalls or bad documents printed and thrown out that is 50% or more of the number of usable documents printed.
The official position is that 180051 is a Qt bug, not a KDE bug. Nobody in the KDE project is officially responsible for working around Qt bugs, but various developers have been consistently insulting to users who complain about it. KDE maintains a copy of the Qt tree under revision control for the purposes of working around Qt bugs, but because of a desire to maintain the purity of that copy, and because it wouldn't help the small minority who get their Qt libraries independently of KDE, the existing patch for this bug will not be applied to that tree. First reported in January 2009: two years ago. This is also a regression, because KDE 3 worked. It is currently the highest-voted item on the "most hated bugs" list for the kdeprint module, with more than 14 times as many votes as the second-highest; it is also the eleventh most hated bug for the entire KDE project. In the Qt project's bug-tracking system, it is classified as a "suggestion"; there it was first reported December 2009.