Our X3 has 75,000 km on it, and is now 10 months out of warranty. I sold my X5 as soon as the warranty was over, but I am willing to keep the X3 longer, due to the simpler E46 platform. I can work on it myself, I have access to a full shop with hoist and diagnostic tooling, and I get parts at a discount. With that all said, I still won't own it past about 150,000 km or ten years, and even that will be pushing it. For now, I am figuring that will be the upper limit.

My x3 was pretty trouble free up to about 160k miles when I traded it. It was a 6spd manual too.

It did have the cat issue. We assessed that it wasn't the cats even though the dealer said it was but no one ever figured it out and it ran fine so it wasn't messed with much. (now there is more info, mine was just prematurely high miled because of my driving.) I wish I had kept the thing now and it's hard to find another nice manual out there.