I leave my wi-fi on all the time too, I have a touch 3G and sometimes, when I buy a book from the website, it's on as soon as I turn on the Touch, but more often, I have to "sync and Check" many times until it downloads. If I don't do the sync and check and just wait, it can be as long as 12 hours sometimes before it downloads. Oddly I've noticed If I'm waiting for something, if I connect to the kindle store then press the home button that will often trigger the download. I'm wondering if I have if not a lemon at least maybe a twist of lemon?
There might be some confusion in terminology. Kindles are wireless. You can turn the wireless on or off. Some kindles have only a WiFi wireless connection. Some older ones only have a 3G wireless connection. Some have both. They're two different ways of accessing the 'ether world'.

If you have one that has both, you can tell which connection it's using as there'll be a little "wifi" or "3G" next to the wireless icon at the upper right when wireless is on.
I think with the WiFi it automatically checks much more often. . .after all, any data transfer isn't costing anyone anything extra. But if it's connected via 3G -- which Amazon is paying for -- I don't think it will 'phone home' nearly as often. Maybe no more often than once or twice a day. And it makes sense that if you go to the Kindle store -- Amazon wants you to buy stuff! -- that triggers a download.
thanks.... this helps!!!! I'm fairly new to the world of Kindle, and I thought that I read somewhere that leaving the WiFi on all the time wears the battery down. I'm guessing that you don't find it a big deal, or you wouldn't be doing it.
FWIW, I don't think leaving WiFi on all the time is nearly the amount of drain as leaving 3G on. . .especially if the device is mostly in an area that has a decent wifi signal. It's like it just stays connected. With 3G it has to keep pinging to make sure the connection is still there. . .that can tend to drain the battery faster. My assessment is that WiFi is the best for regular usage, but a 3G connection is nice if you really want to download something and aren't somewhere you can easily connect with the WiFi. . . . assuming, of course, that you have a decent 3G signal.
