It seems that the callouses I'm developing on my left hand -- specifically the three middle fingers on my left hand -- are really playing havoc with my ability to know when I'm hitting a key when I type. I've been a touch-typer since before high school. It's only in the past couple of weeks that I've noticed how much my sense of touch is actually used while typing -- I hadn't thought about it much before, but I would have assumed that touch typing was more about finger position than sense of touch, which seems not to be the case for me. When I type now, I'm hitting the keys with my left had before I seem to register that I'm hitting the keys. I've noticed more instances of being "off by one" and hitting multiple keys at a time since I've been practicing my mandolin.
I fully expect this trend to reverse once I get more used to my newly-formed callouses. I expect that mandolin playing will improve my typing much like piano playing improved my typing when I used to play a lot of piano, for the same reason meep mentioned -- my fingers are becoming more limber and strong. Once I get used to the sensitivity issue, I fully expect my left hand to fly across the keyboard as I type.
Anyway, I've got my fourth mandolin lesson this afternoon. I'm still loving it. So far, I've been learning basic treatments of traditional tunes: The Girl I Left Behind, Liberty, and Soldier's Joy. Last week, Jeff even added a double-stop for a couple of the notes in Soldier's Joy to dress it up a little bit. He also mentioned that we'll be going back to some of the tunes that we're learning now and making them fancier as I get better. All in all, it's loads of fun. I'm finally at the point where I know a handful of chords and can transition between them well enough to provide reasonable accompaniment, which is nice. I'm looking forward to getting together with some friends and jamming a bit. Mrs. Mellow and I already do a bit of that -- mandolin and flute sound pretty cool together, as does mandolin and piano.