It's not so much a matter of "can I?" with me, but rather "will I?"
I've had a Pebble for 1.5 years now and I've showered with it twice. This is a watch with a waterproof rating up to 5 ATM which is quite impressive and makes the watch fully submersible. I've worn it in the pool, however, because it's nice being able to control my music and check texts and phone calls without having to dart out of the pool, dry off, and grab my phone, all the while hoping I didn't miss the call anyway. In the shower? Not so useful.
I'm probably not going to take the risk of showering with my Watch even though it's "water resistant," there's simply no reason to. You can't clean under the watch this way, you risk damaging a $350 device (if you bought the cheapest model, that is), and it's just unnecessary. I'm sure whatever calls and texts I miss while taking my 5 minute shower will be waiting for me when I get out.