My case of woes (until now):
1. never used synching after all the caveats issued here, there and really
everywhere (yep, Beatles day!);
2. I had sometimes problems with "large" files from the Sony store itself
but none with similar-size ePubs: taken up to five-ten minutes, for example, with
this one;
3. try to put more than a couple-fourish books on unit/sd/memory stick and the library will be inexorably stuck. Have to force quit and do it one by one. And without a long queue,
too.