I believe the length of this argument belies the claim of the Sha'ir being "inarguably" Tier 1....
Except that other than a DM interpreting unused spells as being cast (which is a serious problem at low levels if your DM does it), all the arguments against it have been either about things that have no bearing on whether it's Tier 1 (seriously, if scrolls are that big a deal you can take it as a first-level feat) or about things that are factually untrue (the assertion that sha'ir can't prepare spells on the fly when that's their central class ability.)
While the class has theoretical Tier 1 potential, I still think the extreme hassle of actually playing one would prevent it from ever reaching its true potential until the higher levels, i.e. until a spell won't dissipate during a normal adventuring day.
For instance, at level 1 a Sha'ir will need to get new spells every hour, or basically constantly have his gen fetchign spells to replenish those that dropped out. (And seriously, saying the dissipated spells count as cast is ridiculous.)
Now a strict GM could ask a player to actually DO that paperwork, and also mention every time the Gen is sent out. And that... would just kill all the fun. And with rising levels, the player would potentially have to do more and more paperwork, what with rolling every fricking interval for the Gen to get the spell.
That's a mechanic that just doesn't work, as written. The only way to play it would be to say, hey, get your spells in the background, I don't give a damn until you get a spell you don't know or a divine spell.
Also, the Diplo check:
Let's say the Sha'ir has 18Cha at level 1, and 4 ranks in Diplo: The DC is 20. The bonus is 8, +1 for level 1, +2 for a known spells, -2 for a level 1 spell = 11. That's just over 50%. And don't tell me I should take a crappy feat (with the possible exception of Nymph's kiss) to improve that chance.
At level 10, the Shair has, say, 24 Cha, and 13 ranks. That's a +20 bonus, +2 for spells known, +10 for Shair levels = 32. So at level 10 you can definitely get a level 5 spell known (-10 to the check). For an unknown arcane spell, you still get it. For an unknown divine spell you're back to rolling, after having to wait for X hours for the spell. (And a 5th level spell could take 11 hours to get!)
So while that mechanic is marginally better than a Truespeak DC, it still sucks.
The class is interesting, and has high theoretical potential, but only if you actually REMOVE all the hassle involved with it. In which case it's just a Tier 1 wizard with access to some divine spells.
Both problems can be largely mitigated by taking 10 on your Diplomacy check. If you pick up one or more of Diplomacy's synergy skills (Bluff and Sense Motive are both on your class list), you don't need Diplo-increasing feats to reliably pick up unknown spells after first level. The sha'ir does face minor MAD in this regard: you basically need a high enough Int to have extra skill points, because they're mechanically reliant on three skills, benefit from having skill points beyond that, and only have 2+int per level.
There could be a lot of potential bookkeeping involved with "what spells did I get when", although it's only likely to be an issue if you get attacked exactly X hours after your last major load-up.
So, I'm reading it over... it only casts on the Sorc/Wiz list plus a few hard to get divine spells (didn't notice anything amazing there). It's basically a Sorcerer that then has access to the rest of the list, very much like a Sorcerer 5/Master of the Arcane Order 10 might have, really. That seems pretty straight forward. You also get a Planar Ally ability for genies, but considering you have Planar Binding anyway I'm not really sure what the point is there.
Also, note that the spells per day are spells cast, not spells retrieved. I'm pretty sure if you let the spell go without casting it they don't count, per RAW.
JaronK
It's a little more like a Cha-driven wizard than a sorcerer in my opinion, since it fetches spells in advance and the "spells known" don't have a major impact on what spells you can actually prepare. The advanced class abilities aren't terribly interesting. As for the divine spellcasting, there are a couple of potentially interesting things on there (Find the Path, Miracle) but mostly my inclination is to ignore the divine spells except as an easy route to qualify for divine PrCs (Skypledged, Contemplative, Dweomerkeeper).