I'm not an expert, by any means, but I wanted to bump your questions up to the front of the queue.
I've noticed that using my Memory Stick causes a quicker depletion of the battery. There is a slight delay after I install the memory stick when the reader is loading and I've also noticed a slight delay upon opening a new ebook from the memory card, but other than that, I haven't been aware of any page turning delays.
I've had a great deal of problems when disconnect my reader from ELS. If I just unplugged the reader from the cable, it causes my reader to freeze and I have to do a soft reset. If I eject the reader using by selecting the eject button on the ELS screen, ELS freezes and I have to do a hard shutdown on my laptop and reboot the entire system. I've spoken to Sony support about the problem but the suggestions they gave me were useless.
As for cleaning up my ebooks, I don't delete anything. I'm an ebook pack rat!