MikeFerrara:
You can write anything in your log that think is of value.
When most folks ask "do you 'log' thus-and-such?", they are implying logging the event
as a dive and as such, I wouldn't 'log' a pool dive. However, every pool training session I do, as either student or instructor, is in my logbook to document the skills each student performed (or the ones I performed if I'm in the pool as a student). Those sessions aren't logged as dives - that is, they aren't 'counters' - but especially if I'm instructing I want to document what we did, and the logbook's a convenient place to keep that.
In keeping with what Mike says, some of the other things you may find in my logbook from time to time are beer labels, receipts from particularly good restaurants, calling cards from divers I've met or other interesting folk... Phone numbers, a calendar, weighting chart, tank specs, tables etc...
If I'm just in the pool practicing something I don't usually put that in the log book, but if I discover something worth documenting I'll stick it in there.
It's your logbook - put whatever you want in there that you think will be useful to you.
I like to use a loose-leaf (I use the SSI format book) rather than a bound book, so as it gets too full I can remove the pages that have the least relevance and stick 'em in my "logbook" drawer. That also lets me put pages specific to a particular destination back in when I'm headed there.
I use my logbook so much now that I
really wish I hadn't waited 25 years to start one.
Rick