Just had one a few weeks back. Don't hold your breath for the next one. Maybe in 6 months or so (there is an Anniversary coming up in 3 months that some of us are hoping to see some deals). They rarely do gem sales in this game. Remember, frequent gem sales usually indicates a game in financial difficulty unless it is a designed part of their usual game economy. If you start seeing too many gem sales, It might be a clue to avoid buying and start following the other rats fleeing the ship.
Not necessarily in PP, but in many other freemium games, this does hold a bit of weight. Some start off already having crazy constant sales and just continue that the entire life of the game, but for a game that starts off without many sales, a sudden influx of them usually either accompanies a downward trend in revenue and player retention (thus milking players hanging on to it as much as possible before the game finally dies), or it happens alongside a change in staff at one of the involved companies, as a new marketing manager could have a different strategy. If we don't hear news about rovio or midoki staff changing, then gem sale frequency may be a decent metric of the financial stability of the game. However given that Rovio recently let go a lot of employees and to put most of their focus into the angry birds film, staffing change could very well happen now that the movie is out. Regular sales aren't not-beneficial, but I'm sure whoever's in charge of marketing pays very close attention to analytics and has a good strategy planned for economic success.
I agree 100%, I think regular gem sales would benefit a game. Other games I play which offer frequent sales, I always wait for the sale to buy. Only problem, in my mind I am thinking the sale price is actually the regular price, and the regular price in those games are actually over inflated prices. So buying on sale is really paying normal price and in reality those games never really offer a sale. At least in this game, with the infrequent sales, I feel I am actually getting a discounted price on gems, not just a con job like the other games do. But guess I am just weird in that way.
Personaly I don't need Olen's sales often but if you know there are two fixed moments troughout a you I would stack up. 19th of September Midoki plunder pirates celibretes it's 2nd birthday so I have high hopes. Also: my second account DOES get the 20% off gems sale offer every now and then. Even though I bought gems in the past. Normally this means the Gems purchase with discount options does not show ever again...