This is only a minor improvement.
If you set the threshold to low (a few minutes), you'll be very annoyed by entering your code dozens of time a day.
If you set the threshold to hight, you'll be very very annoyed when you lose your N900... ;o)

And locking your N900 doesn't mean that you cannot access the hard drive data by other means...

The only problem in "remote locking & wiping" is that you have an inevitable delay between the lost and the lock&wipe (you have to be aware of the lost).