I like that you comment on comments. Here is are some things to study hands on in my 2k-view (senseis and eidogo. It's all there. It won't take you long). I talk from my experience (and there are reasons I am 2k and not 2d). So if this is b**s, I am happy to be corrected and learn something myself. Don't let Fedya pick up bad habits from me.
Fedya wrote:
First, I don't think I would ever have thought of those second-line moves that skydyr mentioned when I played the 3-3 invasion on

.
Well, you should. It is one of the easy joseki, so there is no excuse. No branching, all quite natural and easy to remember (you have to form a L+2 group with sente moves). Senseis is probably your friend here. And if you don't know about the L+x groups, then that's also homework.
Fedya wrote:
When I played the ko to save those stones, I wasn't thinking about just the few stones in the corner, but the fact that White would otherwise have almost a sixth of the board from A1-J7.
White already had most of that sixth of the board anyway. The stakes are only the points in the corner and their future potential (and the potential is nil apart from the cutting stone on D5, so we're basically only talking the points here). For the rest of the points that make up the sixth of the board you got some compensation elsewhere before (you should have). And for the points in the corner you get 2 moves elsewhere (actually 3 because of the double step ko). The deal of letting them go is to your favor.
Fedya wrote:
P9 on

is the sort of thing that doesn't look big to me at all, and looks like it's just going to wind up isolated and floating with no way to get eyes.
I have the same feeling here. But mostly because black has to create a MOAB size ruckus to win this game. I prefere reductions when I feel ahead. Isolated stones are no problem as long your opponent answered them on the inside. If they got answered on the inside you can let them go (maybe they were aji keshi and wrong to play, but once answered on the inside they have done their deed). That's one of the few things I blindly trust and would prefer to understand properly. Hopefully when I'm stronger. Not really satisfying, but it never let me down.
Fedya wrote:
Bayu: You're suggesting that the good reason to play a pincer on

is because I have a stone in the top right, and not because, well, I have no other idea what to do? As you can see, I still have difficulty figuring out which joseki to play in any given situation.
Picking a joseki comes a move later. First thing is deciding on pincer or not.
A nice thing about hoshis is their property of working great with pincers on both adjacent corners. That's oversimplified, but still. If the top right corner were white, your pincer would end up with fewer friends and the resulting group would be under heavier fire. A pincer might still be correct, but you have to face the consequences. Pincers usually create weak groups. Hence I prefer pincers with some back up (I keep the ones without friends for emergency tactics).
Fedya wrote:

No, I obviously don't know what I'm doing.

If I did, would I have played that move?
The move is not so bad if you know what you're doing. Check it out on eidogo/Kogo. And your opponent fell for it

I hope I wouldn't have fallen for it myself, but I wouldn't bet on it.
For all the close pincers to hoshi and 3-4, it's quite handy to have a single joseki line memorised (4 in total. It's not a phone directory). You can still deviate (and if you see a reason to do so, you should. Or your opponent will take you by surprise) but it helps to add more lines to your repertoire when analysing your games as you can put them into relation with something you already know. I often don't know neither which joseki to pick (if I happen to have to pleasure to know a selection of josekis to choose from, that is). I made up my guidelines and I'll study this at some later stage when there is need or interest. (There is always the fallback that you can choose a joseki you think the opponent won't know neither) It wasn't an obstacle for me to overcome 6 kyu. Your average joe opponent is probably as clueless. I don't see a deficit here.
If something sank it might be a treasure. And 2kyu advice is not necessarily Dan repertoire..