I've mainly noticed the freezing behavior in the following circumstances:
* X-ecuter 2.x Lite or 2.x Pro running the x2_4977 BIOS
* EvolutionX as the dash
* Network cable plugged in and active, static or dynamic IP from router on LAN
Generally, apps freeze almost immediately after they begin to load, namely emulators (such as FCE -- any version) and some games (Tony Hawk 4 will freeze every time during the intro movie after the game loads, sometimes Halo crashes). The crashing occurs consistently when the XBOX is first powered on (with the network cable plugged in) and x2_4977 is loaded from the modchip. Once the freeze actually occurs (in any of the apps or games that have the problem), powering the XBOX off and then on again completely eliminates the possibility of it happening again, that is, until you shut down your XBOX and turn it back on after an extended period of time. If you leave the network cable unplugged, the freezing behavior will NEVER occur, regardless of the circumstances.
So, as a general rule, if you have the freezing issues with x2_4977, don't run the games & apps that freeze when the network cable is plugged in. Technically, you only need your network cable plugged in for FTP purposes or for online gaming (system link, xbconnect, XBOX Live, etc.), so leave it unplugged. Otherwise, if you absolutely MUST leave your network cable plugged in (for online gaming, etc.), let the freeze occur once, shut off the XBOX, then turn it back ON. The freeze should be gone in either scenario.
IGR either works or it doesn't depending on the game and the dash you're running. The freezing behavior that I mentioned above seems pretty unrelated to IGR, as enabling/disabling it does not have an effect - games will still freeze when the network cable is plugged in regardless of whether or not IGR is enabled or completely disabled.