I keep track of coin weight for my characters, and while it's a hassle, it's not really
that difficult to multiply total number of coins by 0.02 to get weight in pounds. I guess I've always enjoyed that little bit of extra realism ("I
told you that bag of 500 coins would slow you down."), and there's an historical game element, in Gygax's choice to give huge amounts of copper as treasure ("Tell me again just how you're going to carry that out of the dungeon?").
There are ways around it. RA spoke about converting to platinum ASAP. Personally, I like gems (a part of the game underused in the my experience) but as Somone pointed out, letters of credit are another way around it (just so long as you don't expect the innkeeper in that out-of-the-way place to give you
change).
Of course, if you have all your funds tied up in a single, highly portable unit such as a gem, it would be such a blow if some rotten so-and-so stole it from you! But then, surely only a RBDM would even consider such an underhanded ploy (all in the name of roleplaying, of course).
Oh well, I don't really mind either way. Just wanted to point out that the idea wasn't wholly without merit.
Mind you, one way to simplify might be to round down to the nearest 50 coins. That way, we'd only have to deal with whole pounds (as opposed to halfpennies

)
'Nock