With the advent of multi-core processors, CPU bound applications need to use multi-threading in order to be able to scale their performance beyond that offered by a single core. This provides many challenges, but an interesting aspect of this problem is to consider how the threading modules in modern programming languages such as Python and Rubycan either help or hinder this scalability. Yes, there are plenty of other programming languages in use today, but Python and especially Ruby are rapidly rising in popularity and there are some surprising limitations to be aware of when using their threading packages.