I have 75 Ghashes on Cex.io. It gives +0.04 BTC per week, it gets ROI for 5-6 months. Also, you can always sell your Ghashes.
It won't even ROI in 5-6 years.
Plus, the maintenance fee they don't advertise on the front page is currently a completely ridiculous
19.68%. And it keeps climbing.
By now, you'll lose ~50-75% of your total investment in 5-6 months - guaranteed. If you call that "ROI" then it's back to math school.
Advice = sell and get outta there ASAP, unless you want to observe your invested net value decrease every month for some reason
(note - I assume you forgot the diff increase that reduce your income every 2016 blocks solved worldwide, roughly every 10-12 days; additionally your contributed shares will create less and less output due to permanent pool hashrate increasing, thus reducing your percentage and reward portion of the pool's total)
PBmining on the other hand could be a ponzi that could blow up any single week, since the calculations don't add up (they'd make serious losses with their longer running contracts). Add to that the bought spammers praising it with no substance whatsoever, you get the picture. Low return (at least it has potential to actually ROI) but High-risk.
Overall, forget mining. Mining is for the suckers, unless you have access to very good deals in high-end gear AND have access to dirt cheap electricity.
Instead, buy BTC at a price you like and be done with it. Saves you from taking lots of risks AND money. And you have the BTC you wanted.
if you
have to (i.e. to make the learning experience), absolutely minimize your investment and take that part as a hobby.
Mining = lots of risk exposure over a long period of time, lots of unknown variables,
extremely likely to lose you money (translates into taking a 1000mi detour to your destination through a dark wilderness)
Buying = minimum risk, entry point and timing (price) is your choice, done... (translates into taking a 5mi highway segment straight to your destination)
