Actually, in the case of applications, you don't even need to bother contacting the iTunes Store Customer Service. iTunes will allow you to re-download any applications you've previously purchased at no charge. Just attempt to buy the app as you normally would, either through iTunes or directly on your device and iTunes (or the App Store on your device) will pop up notifying you that you've already purchased the app in question and notify you that you can download it again for free.
Note that if you've purchased apps on your iPod touch directly and are using manual mode with iTunes, your apps remain on your device and may not automatically sync back to your iTunes library. You can manually transfer your apps back into iTunes by right-clicking on your iPod touch in the iTunes Devices list and choosing "Transfer Purchases." This will transfer any content purchased on the device, including media content, back into your iTunes library, provided iTunes is authorized for the iTunes Store account that was used to purchase this content. If you're using automatic sync with your computer, this should be taken care of automatically, but note that you still need to ensure that you have authorized your computer for your iTunes Store account. Your computer should be authorized if you've ever purchased anything directly on the computer, otherwise you will need to go to the Store menu in iTunes and select the Authorize Computer option.
iTunes can also back up the data stored on your iPod touch so that this can be restored back to your device (or even a new device should you ever need a replacement). This data contains not only the settings for the built-in apps, but also any third-party apps that you have installed. If you're using automatic sync, these backups are created automatically whenever you connect your iPod. In manual mode, you may need to backup manually; this is done by right-clicking your iPod in your Devices list and choosing "Back Up."
You can also confirm that you have a recent backup by checking the Devices tab under your iTunes preferences. A list of all devices that have been backed up to your computer will be shown there, along with the date and time of the last successful backup.
Note that these backups are maintained for every application on your device regardless of whether the app itself is in iTunes or not. The applications themselves are not backed up, but their data is. So, even if you have to re-download the app and re-install it, you can still get the data back if you have a recent backup.