I wanted a sleeve for my Dell Inspiron E1705 (which is basically the same machine as the Inspiron 9300/9400) but couldn't find many good reviews online. Some said it would fit in XYZ sleeve and others would say it wouldn't fit in the same sleeve. So, I traveled to a few local computer supply shops and found several things. First, OfficeMax/OfficeDepot suck for laptop sleeves. They have lots of briefcases.
CompUSA (which I generally hate because of their return policy) at least had a decent selection of briefcases, sleeves, and psuedo sleeve-briefcases. I already have lots of bags - I didn't want yet another briefcase or even a briefcase-sleeve combo. I just want a sleeve that will protect my machine inside of whatever crazy bag I may slide it. I tried out the inCase 17" neoprene sleeve which was in the Apple section of the store because it's "for the MacBookPro". In fact, it works great for the Dell Inspiron 17" series machines even though the Inspirons are much fatter than the MacBookPro. I don't usually zip it up because it seems unnecessary and is a bit of a pain. I have to pull the neoprene pretty tight to get the zipper to close so I just don't bother unless I really want to secure it (e.g. sticking the laptop in check-through luggage).