It's a colossal pain trying to build reputation separately on each Stack Exchange site. The reason for this is supposedly that expertise differs across different subject areas. The common rebuttal is that most privileges are based on trust. My proposal is to split reputation into "trust", which is common across the entire Stack Exchange network, and governs things such as asking questions and commenting; and "expertise", which governs things such as answering questions and upvoting and downvoting, and is site-specific. This would make Stack Exchange less restrictive without diminishing quality.
A second problem is that new users often create answers on questions because they have insufficient reputation to comment. Reputation to comment really needs to be reduced.