Multicast and switches
Not all switches are equal - some support multicast better than others.
Although many vendors claim multicast support (ie: IGMP) on their switches sometimes this is less than optimal. Generally speaking newer enterprise class switches (ie: Cisco 3750, etc) will work flawlessly. However if your budget doesn't reach that far then be careful when selecting 'pro-sumer' switches. Experience has indicated that some switches will not pass ~ 6Mbit/sec without periodically dropping packets; while others will work but only up to a hard limit (ie: < ~ 30Mbit/sec). The later case generally won't be a problem at the edge, however in the core a more robust switch is required.
