Personally, search is one of the biggest issues I see needing to be tackled on Steemit. Example of this would include being able to search across multiple tags to better refine the returns (which is possible at http://steemshovel.com/) as well as being able to filter a specific authors blog across one or more tags. Ideally this could even include being filtered on non-tag items such as vote count and/or payout especially once things have fallen off the 24 hr and 30 day periods.

Trying to relocate that 'one really good guide' from some months back is extremely difficult through google.

The other major piece that I hope to see completed soon (I know the dev's have been working on this one for a while) is the major updates to the Steemit editor itself. This is slated to include direct image uploads (so users don't have to user 3rd party hosting sites like steemimg.com or imgur) which is much more akin to what they are used to on say Facebook/Reddit as well as including buttons for centering/alignment. These two additions alone would allow formatting (as I like it) to be done without and html tags or markdown. While this hasn't necessarily been an impediment for me, it would greatly help with onboarding since they wouldn't feel like they are having to get over a learning curve, most people are comfortable using a MS word/wysiwyg looking tool already.

We are definitely moving in the right direction as you can see many of the items from @timcliff's wishlist already existing on here:
https://steemit.com/steemit-ideas/@timcliff/the-steemit-wish-list-avatars-notifications-multi-language-support-and-more-oh-my-v2-0