Lambda expressions are cool. Linq is cool. But Lambdas and Linq can be a quazi-pain-in-the-ass when it comes to inspecting and debugging the process flow of your application.
Remember regular expressions?
"Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems."
A famous quote from Jamie Zawinski. Regexes are cool. You can do a lot with them, but the trouble is that you can do a lot that you really, really shouldn't with them.
Linq and Lamba's fall exactly into this category and I fear in a few years of misuse and abuse, people will be shivering at the sight of Lambda the same as they slink away from regular expressions. I've already seen several examples of Lambda expressions that make my skin crawl.
One common Lambda misuse is the same damn misuse you see with looping structures. "x", cursed "x". And when "x" is used up, you start to see "y", "t", "i", and other letters popping around inside complex nested lambda expressions. I even started doing it myself and then I decided that I deserved a punch to the head if I continued this nonsense.
"x" kills readability.
Lambda is also tough to debug, and unfortunately even with VS2010 the debug windows (such as Watch) still cannot compile them, and they probably never will. The issue with Lambda as I see it is that it is a very powerful and useful tool, but just as prone to misuse as regular expressions. A word of prophetic warning to developers out there: "Just because you can do something with Lambda, doesn't mean you should do it with Lambda."
"I've got string input... After it's been massaged, squeezed, filtered, and transformed by my uber Regular Expression I... I'm not getting the result I'm expecting... WTF?"
"I've got data... After it's been massaged, squeezed, filtered, and transformed by my uber Lambda expressions, I... I'm not getting back the results I'm expecting... WTF?"
I can't tell the difference, can you?
Let me be the first to coin the phrase:
"Some people, when confronted with a problem, think 'I know, I'll use Lambda expressions and LINQ.' Now they have two problems."