I just found an interesting quote by Thomas Fuchs, the creator of script.aculo.us and a core member of the Prototype team. The quote is from his Setup interview:

For computer programmers, especially if you’re self-employed, there’s no excuse whatsoever not to get the latest and greatest. You don’t really have other expenses anyway, it’s tax-deductible and, most importantly, it will make you happy and more productive if you know that you’re using the best available tools.

Do you agree?