Bandwidth required for Bitcoin going global?
This is a possible issue.

Currently we have a block limit in size of 1Mb although many pools send out 250Kb to make their block propagate faster to avoid orphaned blocks.

This gives us a cap of 7 transactions per second, data usage of 6Mb per hour or 144Mb a day, almost negligible amount of bandwidth. 

Visa on average handles 2000 per second.

So looking at 285 times the amount of transaction is using 40Gb per day in bandwidth.

Most home ADSL2 lines can handle this now.