Are you starting from a config that autotune is detecting? Try whatever it finds, then work from that. If just the -l F#x# that autotune chooses doesn't work (and you're using a lowercase L, and you have an updated cudaminer version), you'll need help from cbuchner.

Skimming this thread earlier, there's a lot of mentions of
-l F
-l K
for autotune with a selected kernel, leaving out the specifics (not sure what the #x# represents). Maybe you need a capital F. If it doesn't work, just try -l auto and it'll choose a kernel for you. It says which one it chose in the command prompt as a full descriptor like
K98x2
. You might be trying to use a kernel that's not supported on your card, and using autotune will give you a starting point.

I ran into a weird issue trying the Titan kernel on my GTX670. It was reporting almost 400khash, but every share was being invalidated by the CPU, besides otherwise acting fairly normally. Maybe there's an improvement to be made somewhere that could let Kepler achieve these kinds of khash rates.

For anyone looking for a config for their GTX670, I'm at 180 khash with these settings. If someone has something better, I'm all ears.
-i 1 -l K98x2 -C 2 -m 1

This. Describe where this coin is being invested, besides "with us".

I think the problem right now is that there's a substantial number of people investing into BTC as a speculative venture rather than as a currency. If someone is speculating on the future value of coins, they're coming in with a completely different mindset than someone who believes BTC is a currency, and will push up prices along the way. Once the speculative bubble bursts, BTC needs people to actually use it as a currency to buy and sell things in order for it to survive long term. This means it needs to be used for more than a few niche places in real life, a couple of illicit marketplaces, and as payment for ASIC mining equipment - which isn't the case right now. Until it is in use in a widespread way in physical locations, it's ripe for speculators to abuse.

Anyone holding BTC for a long period of time with the expectation that it will gain value on it's own is a speculator. People need to spend money, not hold onto it in a mattress. When it comes to currency, circulation is highly important, and any given successful currency needs to have a strong incentive to spend or invest rather than save in a mattress in order to provide the actual value associated with every currency - a means of exchange that is more convenient than barter.

Unfortunately, BTC (and other crypto) have a massive problem with the incentives for mining. They all make the assumption that people will mine because the coins will be worth more in the future than they are right now. Without this incentive, you don't have miners in the first place. With this incentive, you have a bunch of speculators involved with BTC until the last coin is mined.