I think there are settings that dictate when the phone checks for updates, you may have it switched off.
Just a note though. You don't get the update over the air and the version of the SE tools installed on the phone won't let you update either. You need to install the latest version of the SE tools from the SE website for it to realise you can update.
One thing to note. I almost lost all my contacts as the SE backup application only backed up contacts I had added on the X10 not the contacts on my SIM card. Make sure you load any changes to your SIM contacts back to the SIM and make sure you have a note of all your numbers