Don't install things to the card.
Sounds like there is confusion here between program memory and device storage. Your device will slow down if you have too many applications running at once (using up program memory), but that has nothing to do with where they are installed (device memory vs. storage card). Accessing the storage card, whether it is to retrieve emails stored on the card, or because you installed a program on the card, will be slower than using device memory to do the same thing.
If you want to speed things up, keep things off the card that you access frequently - particularly email, turn off Manila (huge memory hog), and use the task switcher frequently to close applications that you're not using.
Sorry Jonlee83, I just disagree...nothing personal.
