I have multiple clients using express editions in production environments.
Despite the restrictions there don't appear to be any issues as long as they stay below the 4-10gb database size limit.
My lazyness causes me to try to talk them into using at least a standard edition so I can utilize the tools as needed but, as I said, that is lazyness rather than anything else.
“Program (pro’ gram) n. a logical sequence of operations to be performed by a computer that usually results in error messages, v.t. to engage in an activity similar to banging one’s head against a wall.”