I got rid of pretty much everything my past relationships gave me except for 2 teddys which are stuffed in a cupboard somewhere (Dont want to just put them in a wheelie bin, might take them the charity shop) because I was over them, they didnt bring back particulary good memories for me. I dont think my boyf would have liked me to have them all around the room either. I wasn't with my past boyfs for that long so that could be why.
I think if you have spent years with someone, given so much of your life to them then yes, I can understand why people would hold onto the material things but if it was only a short relationship I wouldnt see the point.
Everyone is different though, and if they do really want to keep the things have them put them away somewhere, they don't need to look at them everyday, if they do then I think theres a problem in there somewhere