Talking about investing Bitcoins, where the return is in BTC is interesting and I have put thought into it.
I am actually offering a high risk, high gain investment in one of my service threads that pays in BTC:
https://bitcointalk.org/index.php?topic=345782.0As can be seen, I show proof of being a winning player (extremely high winrate, but small sample size, true winrate is smaller than appears).
I offer various different levels of investment, ranging from 0.02BTC all the way to 0.5BTC. Most likely will stop offering investments under 0.04BTC once I get enough investors to give me some credibility (once good results come out, hopefully leading to bigger clients).
I have yet to have anyone invest.
If someone here thinks it might be a scam, my other thread on another service (he paid 0.03BTC) has already had a very happy client:
https://bitcointalk.org/index.php?topic=341747.0