How many eBooks do you plan on carring around with you? The internal memory will house up to 350 eBooks, and if you use calibre on your computer you can easily manage as many eBooks as your hard drive will hold and add/delete them from your PRS-300 at will. It's one of the most stable eReaders on the market and offeres the best value for the money. Don't discount it just because of the lack of a memory card slot, that shortfall is easily overcome!
BTW, super cute Avatar!