The only problem with the messenger that I can see is it gives the scammers/spammers another avenue to contact people with their worthless information - so messenger will need some pretty good spam control filters, otherwise itl become much like the problem with the memos at the moment... In that regard I like Discored because it it resonably well used and seperate to the Steem blockchain.

As for user alerts - I agree it would be nice to have something inbuilt into Steem - at the moment I use Ginabot which is customisable and works fairly well but it is seperate and used in discord which im not always logged into.