Apple has quietly released a 1.1.5 firmware upgrade for the iPod Touch. The 1.1.5 firmware remains a free upgrade path for firmware 1.1.4 users who chose not to upgrade to 2.0 ($9.95US).

From what we can tell upon first blush, there are no major (or even minor) changes that are easily detectable, which indicates that perhaps Apple has merely tweaked some of the underlying architecture. After all, there were a number of security updates included in iPhone/iPod touch firmware 2.0, so those may also be integrated into iPod touch 1.1.5 as well.

The 2.0 upgrade was released over the weekend and brings support for MobileMe, Exchange, 3rd Party Applications (App Store) and more. Based on early reports, firmware 1.1.5 appears to add no new features but may improve the speed and stability of existing applications. The update is available through iTunes.

Meanwhile, it appears that Apple is currently testing version 2.0.1 of the iPhone and iPod Touch firmware.