i have loaded up a minecraft server onto my one private server. In short, i found that it was a huge waste of my own space and resources and switched to a paid hosting service. I actually did attempt to seriously run my minecraft server on it. It was an Xserve '08 with dual Xeon processors (can't remember clock speed off the top of my head). The biggest issue that i ran into was that the FTB pack was far too hungry for the server that i had. Even to the point that it would be unusable for other file sharing services due to minecraft being loaded. Not to mention the fact that i was the only one playing on the server.
I had a ton of issues trying to get things set up the way that i wanted on the xserve. It also didn't help that i am in the process of doing quite a bit of moving (moving from one town to another but all my stuff has been in storage for 6 months as well as I've been living in shared accommodation provided with the people I'm working with, so i couldn't really properly set my server up). So i switched to the paid hosting service and have not had near the same amount of issues as when i tried to run it myself.
Now i have full 24/7 server access to my minecraft server which is nice. And i can quickly and easily change mods, update the entire server or do any other config changes pretty easily too.
So running your own server is kind of fun. And it is definitely fun trying to figure out what the problem is. So long as you don't mind a bit of noise from your server (i know that the xserves are pretty noisy, but if you use something else for a server you might not have that issue). For me, having my own server like that is a bit of a novelty. Especially considering I'm looking at seriously upgrading my filtering system to something that will give me far better access with less hassles to deal with the whole server issue (for those of you interested, looking at changing to a synology NAS system that has built in file sharing as well as software that makes it run like a server in its own right without me needing to do too much work).