Just updated my 997. I don't know how many models have been updated. I assume all of the SI series. Here is what it said for the 997.

Description:
2/23/2009 12:00:00 AM - v4.510 Supports the XM NavWeather accessory. Adds new 2D sonar processing techniques, including the ablity to turn off TVG. Adds SI Image Enhancement features. Supports operation of the CannonLink accessory across an InterLink accessory. Modifies the Depth Offset menu item to shift the sonar image, not just the digital depth. Expands Water Type selections to include deep and shallow salt water. Adds Waypoint Decluttering control. Adds Demonstration mode menu item to disable point-of-sale mode when using a transducer with no thermistor. Fixes the color of shoreline construction on Navionics charts. Resolves MMC (not SD) access problems.

Prerequisites:
You will need a working MMC/SD reader/writer device attached to your PC and a formatted MMC/SD card.

Instructions:
Download to your computer and use the HumminbirdPC program to upload your unit. You may also copy the uploaded software to an MMC/SD card and then insert that card into your unit to update its code.