On many mining pools/bonds I see things listed as 105% PPS / 110% PPS weekly payout. What does PPS actually mean?
Where I've seen it, it refers to the mining payment method "Pay per share".
This question has an answer that describes what a "share" is.
On some mining sites that have existed, the earnings for a share have been essentially paid immediately. However, this method exposes the pool operator to a possibility of loss in the case that, on average, they find less that the expected number of blocks. This can be made much worse by a large miner participating in the pool and performing a block-withholding-attack. To prevent these problems, most pool operators prefer slightly modified pay-per-share methods of payment, such as SMPPS (Shared Maximum Pay Per Share).
A payment method is not strictly Pay Per Share if the earnings aren't available for payout immediately, or if risk is passed on to the miner. Note also that it may not always be clear how much of a fee is being charged by a pool operator; it can be as low as 0% or as high as 7% (but if they tell you the payment per share, you should be able to work it out by dividing the block reward of 50BTC by the current difficulty and comparing it with what the pool pays).
A pool would not payout 105% or 110% except perhaps as a promotion when it is trying to increase its number of participants and offers an increased reward such as 55BTC per block (ie 110% of what is earned) at its own cost.
Update: The discussion you linked to in your comment is regarding the issue of mining "bonds" where the issuer promises to pay 110% of the shares mined. Each bond appears to be selling for around 0.6BTC, and represents 2Mh/s of mining speed. Given that the bonds are "perpetual", presumably the issuer has allowed for equipment replacement and maintenance costs, and power etc. Payouts are advertised as "currently 110% of PPS", so it is presumably a promotional offer. The issuer must be earning a margin somewhere along the way to cover the cost.
The explanation is that "First, I will be doing merged mining so those coins will be used to increase the pay per share. Also, I would like to offer a good value for each bondholder", however my understand is that merged mining only increases return by 1% or less, so the promoter appears to be offering coins from his own pocket. Would be enough to make me suspicious. Apr 23, 2012 at 23:48
@HighlyIrregular: Where mining bonds are concerned, 110% PPS is nothing more than a cheap marketing gimmick, designed to give the illusion of differentiation for what is essentially a commodity. Offering a 100% PPS bond for 0.3 BTC is equivalent to offering a 110% PPS bond for 0.33 BTC. Whatever the issuer needs to pay for the extra has already been priced into the issuing price, which is generally higher than the operating cost of the issuer. Apr 24, 2012 at 7:51
@HighlyIrregular: PS At the cost of the appearance of shameless self-promotion, I think you're confused about what a mining bond is, and you might want to have a look at the thread where by all accounts the concept of a deterministic mining bond was invented, bitcointalk.org/index.php?topic=65569. Apr 24, 2012 at 8:02
@MeniRosenfeld, I think I figured out how the bonds work somewhat after posting that comment. It's probably worth mentioning that in the case of bonds referred to by this question, one bond is worth 2Mh/s, but the current promotion offering 110% payment makes them temporarily worth 2.2Mh/s for the duration of the promotion. It's not a long term commitment, so wouldn't justify a 10% increase in the bond purchase price though. Apr 24, 2012 at 9:20
PPS is "pay per share", a mining pool reward system where the operator gives a set payment per share submitted proportional to its average worth, regardless of how many valid blocks the pool finds. This way the miner doesn't suffer any variance.
By extension, 100% PPS is the reward that would have been given for a certain hashrate at a PPS pool without a fee. 110% PPS is 110% this amount, etc.
Some pools, for example Chaang-Noi's project, are really pool-hopping proxies so they are able to offer >100% PPS to miners. Things like merged mining, preference for newly generated coins, attacks on Bitcoin or alternative currencies or using the hashrate for things unrelated to Bitcoin - or proxying to gpumax.com, which itself is based on any of the above - can also allow a pool to offer >100% profitably. It could also be a promotional offer.
Some mining bonds state that they pay >100% PPS as a marketing gimmick.