With no doubt , the number of users of brainwallet are less (much less) then the users of exchanges (who stores their coins there) and online wallets but here is the thing , If I learned anything from being with the bitcoin community in the last two years , is that bitcoiners never learn the lesson unless they lose their coins.
I will give you an example , since the hack of Mt.gox and people are advising each other to not store their coins in an exchange but how many of them are actually doing it? not much... because until now , exchanges are still being hacked and we see people crying about how they lost bitcoins.
Overall , you can put reminders and warnings all over the place but If people don't lose their coins , they won't learn the lesson.
I will give you an example , since the hack of Mt.gox and people are advising each other to not store their coins in an exchange but how many of them are actually doing it? not much... because until now , exchanges are still being hacked and we see people crying about how they lost bitcoins.
Overall , you can put reminders and warnings all over the place but If people don't lose their coins , they won't learn the lesson.
I'm just new to bitcoin and don't have a whole one so I don't have a lot to worry about but I've heard stories of people losing their bitcoins. I just found out a relative (who I have no idea is into bitcoin) has lost his. Apparently he got it around 2009 (that's what I heard from another relative, wasn't able to talk to him directly) when they were actually giving away FREE bitcoins. He's got 20, turned them into those paper thingies and promptly forgot about them. Now he's pulling his hairs that they're now worth a million in php. Lesson learned.
We'll all come to a point where we'll have to learn a new storage method but it's really important to put reminders. The worst case is knowing you have bitcoin but can't remember where you stored it. The brainwallet seem interesting but I'm not planning to learn it anytime soon. It'd probably only be some last resort. Even when converted to some mnemonics, it would be hard to remember especially if you have many of these.
Although is not the most secure wallet in the world I use web wallet but on the other hand I don't have much coins. But with time wallets are also developing and getting new features so everyone can choose what suits him the best. 
