Apple has released iOS 4.2 which addresses security issues in addition to allowing iPad users to take advantage of features such as multi-tasking.
Major security issues in WebKit have been addressed including vulnerability and/or bugs related to pre-fetching DNS, memory corruption, CSS counter un-initialized pointer, design issues in handling visited pseudo class, input validation and color cast issues related to SVG documents. Other fixes related to iAd, ImageIO, libxml, CoreGraphics and FreeType have also been addressed. In all a total of 26 Common Vulnerabilities and Exposures are address in the WebKi alone.
Users should update to the latest version but make sure to backup your device before the upgrade.