Another program which should be installed in Main Memory is Agenda Fusion - if it is not, the buttons will not operate properly/at all. Pocket Informant may well be the same.
Screen plug ins too are best in Main Memory, such as Launcher, Calendar Plus, Task Plus and Icbar, Wisbar or Gigabar. All of these are available as free downloads from Aximsite>Other Resources>Downloads (except Gigabar which is freeware from
www.gigabar.com/downloads). Fortunately they are all pretty small.
My Pocket Backup Plus works perfecty from my SD Card.
Built In Storage is best used for PIM info backup and possibly "My Documents". It is ROM and hence not volatile like Main Memory which is RAM and will lose its contents after a battery failure/verylow charge or after a hard reset. If you use Pocket Backup Plus you could probably store a full backup in Built In Memory if you compress it - otherwise there will not be enough room. Built in Memory is not the best place to install any programs.
I
strongly recommeng Gigi's excellent tutorial - see her post above.