On the map with "SpAradise city" the minecarts crashed while we were riding them. We were stuck in nowhere and couldn't get out. This was for everyone using them. I don't believe Notch has bothered to fix that or even knows of it. So that's a pretty severe bug for people who don't know more than getting in and out of minecarts.
Yeah they were fixed after that, when we had to make new boosters because notch had also capped the speed when he made the fix, you could go from SpAradise to Kai city no problem, but then we got an update and stopped using the old map.
Minecarts work, there are some silly things that stop the carts, like putting boosters on a slope, coliding with blocks, or blocks beside but under the cart that are larger than a block, but you can't go wrong as long as you give the cart some room. I just find it quite bizarre that they cause lag issues, more so than personal gateways or redstone, maybe the powered tracks, but all you would have to is put a pressure track down so the all tracks are unpowered until a cart passes over them. I mean they're just tracks, how could they lag of all things? Why does it only appear to be our server that has issues with them? You'd also find no shortage of people who want to lay down the tracks, it's a romantic little feature to the game, and look great when so long as your not doing a 1x1 cobble bridge with them.
Show me these mystical servers with their wondrous cart systems that function perfectly and I will happily go and check them out to find their secret.
Seriously, I'd love to have carts - they are potentially great - but the code is wank. For starters abandoned carts/boats/items left scattered about the map are a HUGE resource drain on the server. While things are abandoned anywhere in a chunk, that chunk and the ones touching it
do not unload. Sure there are ways to address this but they are kinda brute force and have more drawbacks than benefits. Further more the way the carts calculate velocity is just broken, especially if a track goes over a chunk border. Carts stick, jam, lose inertia, stop dead, fall through the floor...the list goes on. Even the core behaviour of the carts is broken. When you travel in a cart you're sending a lot more data back and forth to the server so that you, your cart, your speed and your acceleration can be updated. It should be obvious why they cause lag.
Seriously - find me a server - a real server with a lot of people on it - that uses carts and I will go and see how they do it.
Until then, can we shut up about a feature that even Notch himself has commented on as being broken.