After typing a number of emails and suffering resets twice, I finally uncovered the problem. I'm not sure if this is a known issue or not, but I will check and if not, then post also on SPB's website.

When you use the message preview option from the today screen of an email on SPB Diary, if the "TO" field has to many people listed in it, it causes the device to lock up and subsequently a reset is required. I tried it with a few emails I had from my company's HR department, who always blasts the entire population and each time it would occur. You cannot believe my frustration after having typed like 15 emails on an airplane and then having to reset the device and lose them all. I use the preview option in conjunction with the unread email to determine if I want to respond. Now that I know the problem, I've taken off the message preview option. On a side note, does anyone kno why some emails in the outbox get deleted after a soft reset and others don't? And I find that those in draft always remain after a soft reset.