My wife would never allow me to stick money directly into BTC plus that doing if from here is COMPLICATED (for outgoing international wires) and EXPENSIVE AS HELL on 1250USD wire I'd loose at least 100USD in fees and it'd take hours of time in the actual bank. However building a rig is building a rig and I think of it as at least half the fun plus if the prices drop to 0 you still have the hardware value (ok I know most peeps don't want 20 PCs but still).
As to trading my current average is somewhere between +0.8-1% a day averaged out over the last three months in terms of net fiat. Occasionally I can seriously out do that by adding a bit of forex into the equation as I still have accounts back home (UK and Denmark). With the options Ruxum are offering up, the ability of do serious forex leveraging are going to become INCREDIBLE especially since a lot of them are within one exchange.
As to my ROI calculation on that rig I use the following formula I consider it fairly conservative particularly in view of the recent hashrate drop and using a lowish price in view of recent history. And YUP I was overly optimistic in my previous post I forgot to factor in that you get a new starting point every few days, I built three of these month ago and the numbers were "good" then.
NOTE POWER NOT FACTORED IN AS I BELIEVE THE OTHER FIGURES TO BE VERY CONSERVATIVE AND THE SYSTEM ISN'T EXPANDED DURING THE PERIOD WHICH WOULD ALTER THE EQUATION GREATLY. FURTHERMORE I'M SUPPOSING THAT PEOPLE WILL KEEP ADDING # AT A STABLE RATE.http://www.alloscomp.com/bitcoin/calculator.php
1500 M#/s price 11USD (not too far off I believe)
11 days @ present dif = 96.69$
11 days @ prev dif x 1.08= 88.95$
11 days @ prev dif x 1.08= 81.84$
11 days @ prev dif x 1.08= 75.29$
11 days @ prev dif x 1.08= 69.27$
11 days @ prev dif x 1.08= 63.72$
11 days @ prev dif x 1.08= 58.63$
11 days @ prev dif x 1.08= 53.94$
11 days @ prev dif x 1.08= 49.62$
11 days @ prev dif x 1.08= 45.65$
11 days @ prev dif x 1.08= 42.00$
11 days @ prev dif x 1.08= 38.64$
11 days @ prev dif x 1.08= 35.54$
11 days @ prev dif x 1.08= 32.71$
11 days @ prev dif x 1.08= 30.09$
11 days @ prev dif x 1.08= 27.68$
11 days @ prev dif x 1.08= 25.47$
11 days @ prev dif x 1.08= 23.43$
11 days @ prev dif x 1.08= 21.56$
So 209 days in you'll have a return of roughly 960.72 USD PROVIDED THAT
A) You can't clock super hard. Going up to 1600M#/s should put you @ 1045 USD
B) Difficulty increases don't slow down. A drop to a 4% average increase would put you @ 1304.25 USD
C) Prices remain at this low level. An increase to 12 would put you @ 1048.13 USD
D) You don't add a card after 2 weeks (and yes they will all fit in the case even 6 and stay cool using extenders this is a massive full tower). Adding a card would put you @ 1154 USD minus 150USD for the extra card.
This is how I calculate if it's worth the risk. These are just a small number of factors that may positively affect the outcome of your investment if you start combining these factors to lesser degrees it's fairly clear that an ROI of 5-6 months is possible.