The 1.4.7 patch has brought in a few fixes that have been trialled in the latest pre-release. The crashes caused by using fireworks without a fireworks star in multiplayer and related to arrows fired from dispensers, have now been fixed. Also fixed it the long timeout when checking SRV records.
To update to Minecraft version 1.4.7 simply open the Minecraft launcher and choose the option update now. The update like all Minecraft updates is not mandatory but to use multiplayer players must have the same version as the server they wish to join.