It is here, the 4 GB HD, but is it reliable

The 4GB HD uses ultra-reliable Micro-Drive technology and is being touted as the biggest thing coming for the Spring season is PSP technology. The hard drive interfaces with the PSP by means of a flexible memory stick adapter which is plugged into the memory stick slot on the PSP. Although this is nice and easy it does require tugging along one more piece to the PSP puzzle.
Once connected however the body of the hard drive attaches snugly to the back of the PSP by two location posts which slot into corresponding holes on the back of the PSP. Although a bit bulkier than what PSP users are use to it may not take long to get use to in trade for the larger hard drive space.
Once connected, you use the 4GB HD just as you would a normal memory stick, you can playback video, MP3s, movies and images and save from inside your PSP games. So what it boils down to is how you weigh out this new piece of equipment. My guess is that the trade off of more bulk will even out for a larger home for your material.