I have several acquaintances that have been fired/laid off by email, sometimes while they were at work. I have one close friend that received a diagnosis of Paget's by email (though admittedly she kept having trouble seeing the MD in question in a timely manner - when time was of the essence). And know several nurses that were email "screened" by prospective employers
for staff positions (no, not agency or travelers).
If the OP is well liked, a valuable staffer or difficult to replace, at very least the resignation of the staffer will be a great inconvenience. The manager will have to fill the spot, get staff to work extra weekends (imagine the griping and whining) and deal with training/orienting someone or often covering. If the OP is not a valued staffer, well this makes them look worse.
Nursing is a small universe - everyone talks to everyone. While HR may just give out basic data, managers have ways of finding out the treasure and the dirt on prospective employees, and they have long memories.
In the current economy, it does not pay to act recklessly when resigning.
If the employer had the good grace to interview you/hire you/pay you, the least you you can do is resign in person. Really, hoe hard is that?