I've got a stainless conical, and it's pretty nifty. I've been considering buying a couple plastic conicals to supplement my pipeline just because they're cheaper.
As you noted, one of the most beneficial aspects (at least to me) is the ability to rack off trub and flocculate yeast without moving the beer or exposing it to air.
There are two times that I rack out of the bottom port:
1) Before pitching yeast - After transferring wort from the brewpot to the fermenter, I allow it to sit a few minutes (covered) so that the trub can settle to the bottom. Then I open the bottom valve, and let the trub drain out until it starts to run thin. You don't need to get ALL the trub, just the big chunks that settled out in those few minutes. Once the discharge is running thin, close the valve quickly. You shouldn't have to leave the valve open for more than a few seconds, otherwise you're just wasting beer. I then immediately pitch the yeast and seal the fermenter.
2) After fermentation ends - After fermentation has ended (usually around ~1 week for me), I rack again to remove all of the dead yeast that has dropped to the bottom. Again, you don't need to leave the valve open for long or get every last bit of sediment out, just the big chunks. Usually my yeast comes out is a single "turd-like" chunk. Sometimes with the highly flocculate yeast, it won't come out right away, so you may need to leave the valve open for a few seconds and wait for it (unless a bunch of beer is pouring out). If the yeast is really stubborn, you may have to do it in "steps". If this is the case, I just drop a little bit of yeast each day until there are no more big chunks. However, when given the choice between losing a bunch of beer and letting the yeast stay in the fermenter, I'd rather not lose beer. If you lose a bunch of beer when you open the valve (the runoff is thin), then its probably best not to try to rack off any more sediment or dead yeast. After dropping the yeast, you let it sit in "secondary" (really more like an extended primary) for your desired length of time. Usually just another week for me, as I do my aging in the keg.
When it's time to rack to your keg or bottling bucket, then you use the middle valve, which will keep you from racking off the sediment that has collected at the bottom of the cone. Not much to it, it's really pretty simple. I personally like the conical far more than the buckets I used to use, though cleaning them and sanitizing is a bit more involved.
Hope this helps.
- Hunter Q Lafive III, Esq. BA, MBA, CPA, PhD, A++, PMP, ASE, IS0 9000 and Y2K compliant
UnderCouchers 4 Lyfe