Steve McConnell (Code Complete) does a great job of discussing the concept of Technical Debt.

"The term 'technical debt' was coined by Ward Cunningham to describe the obligation that a software organization incurs when it chooses a design or construction approach that's expedient in the short term but that increases complexity and is more costly in the long term."

http://blogs.construx.com/blogs/stevemcc/archive/2007/11/01/technical-debt-2.aspx