If yo do a hard reset on your device, the answear is yes. But, it won't delete the content of your sd/card.
do a back up of your files before you do a reset..
before you do a hard reset try to minimize the amount of apps, photo etc that you have on your device, start by seing on how much of it you can transfer to the sd card.
And start playing with your device setting, and see what you can get away with without ruining your device.lol i, e, lower brightness, check how often your device sync etc.
Have you tried re-booting your device?
I recommend checking your Facebook setting by pc, go to your fb account and start looking at edit friends. account settings, privacy settings and if that don't fix it theres a fb help center.
And Useless is a harsh words, i prefer the terms learning.
If none of the above helps, get in touch with the HTC and inform them of your device delemma, since theres a lot of HTC Legend with the same problem after the froyo update.
Let us know on how it went and good luck