I'm of the same mind as myntvary, but IP changer usually makes me feel at least a little bit safer. I use HMA ***, it costs like $11 a month or so. One thing to note is that it WILL slow down your internet, so you may experience some problems depending on your net. Me, I have crappy internet, but usually it's not a big deal (I run 8mb net atm >.<). Also, I use Pingzapper for tunneling, which may improve or may slow down. Both of these methods work better some days than others. And also, Tunneling DOES NOT change your IP.
Personally I never use GrindBot. Read in a lot of threads that it's unsafe so I stay away from it. But a few hours should be fine I guess, probably more lenient towards it if you're grinding mats.
I also believe Blizzard don't really ban us botters anymore unless they need to make an example out of us or it's just too hard to ignore. Blizzard needs all subscribers and all players they can get.
And TIP of the Day!
A little common sense goes a long way in botting