First Sign Of Problems: Prefixed Columns
Do you have columns with similar prefixes?
I took the Users and Posts tables from Stack Overflow and mangled them a bit to look like this.
You may not have tables with this explicit arrangement, but it could be implied all over the place.
One great way to tell is to look at your indexes. If certain groups of columns are always indexed together, or if there are lots of missing index requests for certain groups of columns, it may be time to look at splitting them out into different tables.
These things tend to happen, but they can have serious negative consequences for database performance, not to mention the risk of bad data sneaking in.