What is the practicality of it? It seems to be kind of blown over on the forums and I'm guessing because it's something which takes a lot of time and resources and yet really isn't that great.

Anyone here use it regularly? How, where?

Tracks take time to put down, you need a fairly large amount to cover any useful distance, and for the best effect you need to make a horizontal tunned across the map. I would not be surprised if many consider it too much effort for too little gain. Also, some people are a little annoyed that a bug involving boosters got fixed, which stops the cart from going inanely fast.

Still, it can be fun to mess around with them, so try them out on a world you wish to keep as a more permanent base.

If you don't get bored, while travelling from one point of the map to another on foot, don't waste resources.
I'm playing in a huge map, I find it very useful. Not only for travelling fast, but because I'm in Hardmode, so I have to be careful, because some enemies are very dangerous.

It's more useful in large worlds since traveling from one point to another takes much longer, for example it can take me(on foot) to almost sunset to hoof it from my base to the dungeon and that is leaving at sunrise. So having a faster mode of travel helps, I kinds made my own little minecart subway system under my base, planning on mixing it with Teleporters once I go into Hardmode and acquire the Steampunker. The plan is I will use the Minecart subway to travel set points(to the left or right) and have Teleporters at each "stop" to take me to a certain spot in that Biomes underground, with one special one by my base to take me to my battle arena for most of the Boss fights.