I'm using it on a shared server without any probs. I talked to my host beforehand and he monitored server usage when it was installed. Saw no noticeable difference in bandwidth or server load.
However I've only got a couple of text groups, and I don't yet have the reply function switched on (tho I doubt that would make a difference),. If you were planning on loads of binary groups or dumping thousands of posts in at once you might have problems. Otherwise if you use common sense I doubt you'll give your host any cause for complaint.
Re the question about spammers from your forum: perhaps ensure that only registered users can post and have a moderater check before they are sent out. I've not got round to setting a Cron job yet but it's easy enough to run manually.
Incoming spam you have to get rid of manually which is a pain.
I've not really had any 'hanging' problems - occasionally it takes a couple of minutes to download (when there is about 50 messages) but other than that, no probs. Acts much like a normal forum.
Did have a bit of a scare when someone was posting binaries to the group and it showed up on the thread as an attachment. I'd switched attachments off in that forum, so I checked the DB to be sure. Nothing there, which was a relief!
I had very little probs with it once I figured I needed to get the last message ID from the news source I'd be using (they are all different apparently). I'd been taking it from Easynews via my newsreader, when I was using a free teranews account for yhe hack, and the ids were different. Once that was sussed, everything was fine.
Oh but I did turn off the option to index post for searching (in the gateway file). Had probs before with the search index getting too big so I played safe and switched it off.
As it is essentially another forum, there shouldn't be any problems if you keep it pruned regularly because it'll fill up much faster than a regular forum.
It's a great hack so go for it.
Good luck!