4.2 PL whatever the latest version is on 3 boards. I'm happy with it to be honest and won't be moving ot 5 for a very long time.
Same thing I'm planning as well. I'd rather wait til they fix all the issues that they have, the URLS structure, right now the product is far too new for me to make a decision. I just can't do it.
I'm running 4.1.8. I actually ran every version live from 4.0.2 to 4.1.8 (I always upgraded right when the update came out). Once I came to the realization about a year ago that vBulletin is not a viable long term platform for us, I stopped bothering to upgrade (rather than spend time patching files and doing everything I needed to do for an upgrade, I felt my time was better spent working towards a long term platform).
I'm running 4.2.0 PL2. I usually don't have the time to stay up to date with the vB versions so updating is something I have come to dread. I was on vB 4.1.12 PL2 and was trying to wait it out for 4.2.1 to be released before having to upgrade again but when it got delayed I bit the bullet and upgraded to 4.2.0 PL2.
Nothing is for certain until it happens... But with a little luck, you'll see digitalpoint.com on a different platform soon.
4.2.0 here. Usually keep it up to date, within a build or two depending on the degree/severity of changes.