I don't know, I did a couple games today playing AD, kind of sucked the first one since they had 3 tanks, but the second one, where they were running 2 tanks/kat/yi/teemo, I completely destroyed. Killing with auto attacks for the win. Sword of the occult just makes sense to me, especially when playing low-mid ELO. If I rack up kills quickly then I've got 100 bonus damage for only 1369.

Would heart of gold actually be worth it? Kat last hits incredibly well, and if you're playing mid gold isn't really anything to worry about.

The build I used today in my games was
Boots of speed/2 pots
upgrade into merc treads
sword of the occult (I had 5 kills right off the bat with this)
BF Sword
BF Sword
BF Sword
BF Sword
Upgrade to Bloodstealer
Upgrade to Bloodstealer

This was in about a 45 minute game.

I used to roll with AP on her, but after getting raped by an AD Katarina I gave it a try, and it turned out to fit my play-style much better.

She farms way better than AP Kat, thanks to BB hitting harder, and having a better auto-attack.

You shouldn't really auto-attack enemies with Kat, but if you get silenced or use all of your cooldowns, spending these 3-4 seconds smacking people with your 200+ AD is better than nothing. As an AP Kat, you can't do **** in these situations, 'cept of running away of course.

That would make sense, yeah. That seems to be a problem early game, actually. Last hitting is fine, especially with BB, and actually I can generally own them really easily 1v1 early game even without the added health, but there seems to be a problem getting enough gold to stack mad BF's early game.
also, when stacking bloodstealers, when you get a kill does it just give you the +AD on the one bloodstealer, or say if you had 4 BS's, would it give you the stack effect on all of them when you got a kill?

I like Ap Better because I can get items that sync with her abilities better.

In particular, Abysall Scepter, Void Staff and Rylais.

The rylais definitly makes all of your abilities slow (makes your ultimate more scary) and magic pen just helps. (Can'tslow while using an ultimate and hyaving frozen mallet eh?)

Bloothirster also work on katarina, however it's really a person preference.

AD and AP are both good.

I've played both. AP Kat is better if you have an easy lane. If I have to solo lane I go AD Kat.

AP Kat feels more bursty thanks to Shunpo AP scaling + LichBane. Ult comes out about the same in terms of damage. But consider AP Kat has access to the following... Abyssal Scepter (dive into enemies and they all suffer -20 MR), Zonya's Ring (dive in, Ult, Invuln if necessary), Rylai's (slow on abilities), LichBane (huge burst after every ability).

if people are running away from you then ap and ad ult does the same damage, since ad has more damage per second but ap has slow so the damage lasts longer. but an ad kat's ult hits harder if your team has someone like amumu. (actually amumu's a bad example since he lowers the enemy magic resist so it would be about the same.) as for shunpo since you auto attack once right after it there's not much difference either (not counting lich bane) the main difference that i know is ap has much more utilities (slow, aura, lich bane, etc.) whereas ad is better farmer and can team fight better past her ult.

I had success with a semi hybrid build, building rylai's before or after my 1st bfs, then going to Bloodthirster route. The slow with the high ult output of a AD build really makes sure there are no stragglers. The extra HP is also amazing since you definately will get focused, and can mean the difference in a team fight.