Hi, I'm a Mac user and I've been very satisfied with my Reader so far. My mac is an older G4, running OS 10.4.8.
The SD card method works fine and that's what I use for .pdfs (formatted for the Reader) and .rtf files--just drag and drop.
I have had a lot of success using Biblioskop to write to my Reader directly. There is also a nifty program called "Libriate" which is a Mac OS X GUI for "Makelrf." This creates .lrf files that can have the cover of your book included and the text nicely formatted. I try to run all of my books through this program because I like the formatting and having the cover graphic, then I add them to the reader directly using Biblioskop.
I probably spend WAY too much time finding cover artwork for my books (using amazon, google image search, etc.), but I like having the cover artwork because it makes it more like a "book experience." I'm in the USA and sometimes I like the alternative cover art better and this is one of the cool things about ebooks. I can sort of pick and choose how I want the book to look without too much effort.
At this time, Biblioskop can't transfer .rtf files over to the Reader directly, but I'm assuming (hoping) they will fix that issue in future upgrades. So any .rtf files that I use, I just copy directly to the SD card and read directly from that.
There are other more technical solutions that are mentioned in the forums, but I'm not really bright enough to figure out how to get them to work with my Mac so far.
Once they go to GUI, I'm sure I will be using them a lot since the people writing them are very very good at knowing what they are doing. The guys in these forums rock!
Since I read mostly .lrf files and .rtf files, I don't really have a lot of experience with .pdf. There is a nifty program called PDFLab that I use for images and comics, but I'm not sure it's as powerful as pdfrastafarian (which is Windows only).
The only thing that I have found irritating so far is that I didn't get my $50 credit (since I can't use Connect) and I still haven't been able to delete the free pre-loaded book excerpts and photos that came with the Reader. Biblioskop can delete the files that you have added yourself, but it doesn't read/find the files that were loaded with other programs.
Other than using the $50 credit at the Connect store, I'm not sure how many books I would buy from there anyway. Some people have mentioned formatting issues, so I don't miss using the store. Of course, until they make a Mac version of the software, I can't really judge it.
Good luck!