Do people actually make money at cex.io? If so, hard to argue against market forces. If not, what the heck are people doing???
Lets look at this historical data I got from cex.io thread
These are the closing prices from October 1st to December 27th. Others may fill in the gaps.
1-Oct 0.23000000
2-Oct 0.23849000
3-Oct 0.23000000
4-Oct 0.23510000
5-Oct 0.22400000
6-Oct 0.21000000
7-Oct 0.21790000
8-Oct 0.21730000
9-Oct 0.21700000
10-Oct 0.19120000
11-Oct 0.18990000
12-Oct 0.18478000
13-Oct 0.18180000
14-Oct 0.18270000
15-Oct 0.14250000
16-Oct 0.13399900
17-Oct 0.13998000
18-Oct 0.14039900
19-Oct 0.14131000
20-Oct 0.13890000
21-Oct 0.13180000
22-Oct 0.12200000
23-Oct 0.09500000
24-Oct 0.08266000
25-Oct 0.09090900
26-Oct 0.09750000
27-Oct 0.09980000
28-Oct 0.10427500
29-Oct 0.10410000
30-Oct 0.10600000
31-Oct 0.10748900
1-Nov 0.10760900
2-Nov 0.11046900
3-Nov 0.11999900
4-Nov 0.10050000
5-Nov 0.10710000
6-Nov 0.11411900
7-Nov 0.10517900
8-Nov 0.10189900
9-Nov 0.09445000
10-Nov 0.09638000
11-Nov 0.09582600
12-Nov 0.09110000
13-Nov 0.09099900
14-Nov 0.08100000
15-Nov 0.07920000
16-Nov 0.07990000
17-Nov 0.08097900
18-Nov 0.08074000
19-Nov 0.07866000
20-Nov 0.08402000
21-Nov 0.08205000
22-Nov 0.08199900
23-Nov 0.08400000
24-Nov 0.08499900
25-Nov 0.08661100
26-Nov 0.07974000
27-Nov 0.07680800
28-Nov 0.06767000
29-Nov 0.06599900
30-Nov 0.06879500
1-Dec 0.07150400
2-Dec 0.07128873
3-Dec 0.07210000
4-Dec 0.07308999
5-Dec 0.07399962
6-Dec 0.07986940
7-Dec 0.07699900
8-Dec 0.07555444
9-Dec 0.07237200
10-Dec 0.06949988
11-Dec 0.07118001
12-Dec 0.07389989
13-Dec 0.07397213
14-Dec 0.07346848
15-Dec 0.07189998
16-Dec 0.07257734
17-Dec 0.07232347
18-Dec 0.07187850
19-Dec 0.06999992
20-Dec 0.06769040
21-Dec 0.06861000
22-Dec 0.06795171
23-Dec 0.06239999
24-Dec 0.05619993
25-Dec 0.05664157
26-Dec 0.05127993
27-Dec 0.04988691
I dont use cex.io so I cannot say if it is profitable or not but lets do a simple math using the data above.
Say you got 10ghs on 5th Nov 2013 at 0.10710000btc/ghs totalling 1.071btc.
You let it mine for a month with difficulty 510929738 and got 0.2953btc. I assumed the difficulty does not change so the amount will be less than this.
Then on 5th Dec 2013 you sold your 10ghs at 0.07399962 totalling 0.7399962btc/ghs.
Your profit will be .7399962 + 0.2953 - 1.071 = -0.0357038btc.
I picked the date at random and data for difficulty I got from
http://bitcoinwisdom.com/bitcoin/difficultyIt does not look like a good investment to me. You could increase your btc holdings by daytrading but I wouldnt call daytrading an investment.