I would not recommend closing all apps as a means to save battery, or performance. Apple's multitasking is meant to be for switching apps only, and all memory saving is to be done without the need for the user. Upon low memory, apps are terminated, and more memory is freed. A great explanation can be found here: http://speirs.org/blog/2012/1/2/misc...titasking.html

Mine started going very slow as well when I noticed that I only had 1Gb left.

Deleted lots of unnecessary apps and restarted the iPad and it came back to the normal expected speed... You should preferably delete apps through settings as it also takes anything with it that relates to the App you want to remove.