|laziness, impatience, and hubris|
I would agree that basic debugging skills are worse now than they were 10 years ago, but I would also say that basic math skills have deteriorated. Watch a group of friends try to determine what portion of a bill is theirs, and what size tip to leave and it is obvious. Blame the calculator.
With debugging it isn't quite as simple though.
When I first started programming I would sometimes write the program out on paper, and read through it while keeping track of all the variables. Being able to read code while keeping a mental list of what is happening is valuable when working in a group, but this skill is sometimes neglected due to the ability to run it in a debugger and watch certain variables.
My ideal development strategy is as follows:
1. Write the unit tests as a working specification document. This helps to identify flaws in the intended interface early in the development process.
This strategy leads to loosely coupled / tightly cohesive objects, which are easier to verify with testing and easier to isolate issues when debugging.
A similar strategy can be followed when debugging the code of your team members. Debugging manually is a very time consuming task, regardless of whether the debugging is done through code reading or with a debugger. Use this time more wisely and develop test cases that mirror the analysis you do during debugging.