If you care about making sure the photos are all transferred, you do need to leave it in playback mode (and keep it from powering down if it's set to do so.) The eye-fi service lets you set up notifications (email/SMS/Twitbook) for when items are finished uploading, and it also lets you associate the card with a desktop/laptop running the "Eye-fi center" software that will show you progress as the photos upload (on my Mac, I see the photos and percent complete appear in a mini popup window under the menu bar.) That's not really useful except when you're at home and near your computer, of course, but it is kinda fun to see them pop up on your screen a couple seconds after you take them.