I googled up as much information as I could. Seems the sales as of 2005 were in the top 5 cartridge sales, and Chuck Hawks claims they are still being used actively.
I have 6 of them myself. I'm not a cowboy, but enjoy casting and using the guns for plinking. With the long cartridge neck, its ideal for shooting gas checked bullets out of at regular factory speeds. We have no problem hitting 400 yard dingers and shoot about 3,000 rounds a year just for fun.
The 30-30 is also mild to shoot. Can be shot most of the day in comfort, and is relatively cheap as long as you reload. Its also inexpensive to buy factory and generally will get the job done. I have several fancier guns that are no fun to shoot. They make longer distance shooting too easy.
I'm a bow hunter 90 % of the time, so getting close is the name of the game as far as I'm concerned if I actually hunt with it. I also enjoy the 45-70, 444, 375, 35 Rem., 356 win, and 32 Win. Special.
The lever gun cartridges, and in particular the 30-30 are very popular amongst the casting community.