As for impossible to keep track of? I don't. That is up to my players. That could open a can of worms I suppose. My players can handle simple math. It is simple math. If not, they would not be invited to my table. My players are honest about these things. It adds realism to the game and who wants a guilty conscience of being a liar? My friends do not do that. So I have a table full of good honest friends and some PCs who carry only what makes sense and they all have hired porters.
This would be the main problem for my group. My players probably can handle simple math and I think they aren't intentionally lying to me, but it's still a problem because it's very hard to check because:
1. You need to know the weight of each item. That either means the player has to look up the weight or has to ask me how much the item weights every time he picks one up, which I then need to look up.
2. You need to add together the weight of all items you have. That can be as many as 60 or even more.
When the players first created their character sheets I looked through them for errors, and there were at least 5 mistakes on each character sheet! Wrong weight, wrong amount of gold coins, forgot to account equipped armor into the total weight, etc.
I don't think they intentionally put less weight or gave themselves more coins to deceive me, I think they are just unable to track everything without doing mistakes because they are humans. So in the end I realized that either I have to track everything myself and then just cross-check with their character sheets occasionally or I can't enforce the rules at all.
I can ask my player "This chest weights 31lb including it's contents, can you still carry it?", but he would just say "Oh my, I neglected to track the item weight the past 12 sessions, I first need to get all the weight values and add them together to tell", so unless I want to wait an hour each time, it just doesn't work for me.
Online tools like auto-calc character sheets would help a lot with that, unfortunately I couldn't get my players to use my preferred character sheet as most of them wanted to use MythWeavers so they don't have to bother with unloading files every time there is a change and the MythWeavers sheet doesn't support auto-calculation (not to mention that there are only like 16 lines for items, it was already full with just the list of starting items!).