i've got the same problem and did write that a couple of times in the hope to get some ideas to solve it. i read epub and sometimes pdf.

since it is in my opinion a software problem i just re-installed the basic software, the ..1.0-build1000 and the ..default-content. after that i start the reader and it flips great. speed is good. then i re-connect and put the update-...0629 on it. it still works then ok.
most comment was regarding the SD-card. so, i bought myself a new SD-card and currently it works good. however, the flipping problem come now and then back. i just do the re-install / install trick and it's ok.