1) Some very useful questions such as "what framework would you recommend for parsing CSV in .NET" get closed as "subjective, possibly leads to arguments", whereas they already have a dozen of very useful answers. Had the moderators got there on time, I would not get the info I wanted.

2) Short answers get auto-converted into "comments", so they can not longer be marked as actual answers, even if they are the correct answer.

3) Answers consisting mostly of links to other SO questions with a brief explanation get deleted because "they don't add value". I can't show you them because they got deleted (duh!). That other question/answer might have provided useful context and discussion, or it could actually be the good answer; besides the link itself is valuable as it links two related questions together... In their zeal moderatos actually delete useful information from the system.

4) Security questions overwhelmingly have dangerously wrong accepted answers. SO should admit the shortcoming and ban all security questions (other than pen-testing).

Basically, SO risks becoming another wikipedia with deletionists ruling the roost.