Many people have stated that they have had issues installing the plugins. Some have said they were able to install SQLReports4 as a plugin without any problem. Other have found no work around. Yesterday I worked with a school who found that they were able to install the plugins if they downloaded from a windows computer rather than their mac. Once this was revealed to me it seemed like I should let people know in case you are also having issues.
You can download from a Mac. I work solely on a mac and I have no problems. But I don't use Safari as my primary browser, instead I use Chrome. Firefox is my 2nd choice. Safari a distant 3rd. In my recent experience when I download a zip file with Safari it is automatically unzipped so all I see is the contents of the zip. This doesn't happen with the other 2 browsers and I believe can be turned off in Safari. If you are using a Mac please make sure you download and try to import a zip file, not the xml file inside that zip file. The XML is only the part of the plugin that tells it what to show in the installed plugins list. It is not the plugin itself. The entire zip file is the plugin and that is the ONLY thing that should be imported into the plugin management section.
Hopefully that helps some of you find your issue.