Glad I ordered mine within hours, lot less than 2BTC. Anywho, 'hunt for a psu? Should also do that to cover the possibility of the one in the s4(s) dying. So far mine are running fine but:
The IBM DPS 2kw psu is perfect for an s4. My hungriest one reports in as pulling 1450-1500w from the wall...

That same PSU will feed 3 stock s5's cheaply and odds are will last near forever.. Search eBay for them

On that snippit Doggie spot on. I'm still using the same HP server psu's that I used to run my now retired S1's on, now they run the s3's and in 2 of them together, 3 s5's. So yes, it *is* a one time cost but they live on and on through the generations of miners.

What a load of nonsense! Absolute rubbish!
A PSU is a mining cost whichever way you look at it, I mean, they are not free. If you apply the same logic of the PSU not being consumed during mining (and thus not being a mining cost), then the same applies to the mining rig as it is not consumed during mining either.

On the other hand, if the argument is about the rig depreciating in value fast (due to, amongst other things, new more efficient rigs coming on market etc ..) and that the PSU straddles different generations of rigs, that does not negate its cost, it simply reflects the fact that the PSU depreciates over a longer period than a mining rig. Thus the cost that could be attributed to the PSU is the depreciation in the value of the PSU over the period it is used to power the respective rig.

From only 5 pages back...
Once upon a time the internet was seen as this vast library of reference works to impart knowledge unto all.  Now it seems to be taken over by those unwilling or unable to even search.  Case in point, mental floss on youtube being asked to explain one-way mirrors.  Because a thousand articles and dozens of other videos hadn't already done so...and done a better job at it to boot.rant

S3++ would make a good case for bitmain to consider shipping just boards .... even upgrade kits for the S1 doorstops still out there!

S5 available 6th April on Amazon for UK buyers for just under to GBP 400 (~ BTC 2 at today's rate), free delivery . Not sure whether that price covers import duty (VAT @ 20%).

http://www.amazon.co.uk/gp/product/B00RCTIY4G/ref=pe_186441_65742661_em_1p_0_ti

Only if dirt cheap would I consider going the upgrade kit route again. Did that with 2 of my s1's > s3's and while not exactly hard to do, still a pain in the butt. My time and effort is definitely worth staying with pre-built rigs.

That $20-$40 will soon enough turn into $40-$80 to get it all hooked up .... not forgeting these server PSU's can also die on you then its back to the insignificant $20-$40 .... But we digress, insignificant is still a mining cost, considering you won't be making that in a day!

Its quite a bit more than that, you probably need a break out board and how about the 8 - 6 pin cables you need since most miners use PCI-E cables.  I think you are sugar coating this quite a bit.

Plus PSU's fail when run 24-7 at the power usage we do when mining at the rates we do.    I had 3 fail just last year alone.  Now the only ones I FK with are the g2 SprNovas by EVGA since they honor the 10 year waranty

I'm seeing reference to a S3++.  Would this be an air cooled C1?  Heat a problem?