The rear wheel should not be "slipping" on the SASS. The rear tensioning system is rock solid and completely standard for SS, there's nothing unusually weak or deficient about it. In fact it's the best tensioning system I've used yet on an SS. The SASS uses KMC's el cheapo chain and it stretches pretty easily and wears rapidly. This is probably why people think the rear wheel "slips" in it's dropouts, when in fact it's just the crap chain getting stretched out. Plus newbie SS-ers who've always depended on a derailleur to take care of chain tension don't always appreciate how much even a decent quality chain can stretch while riding an SS, especially if you're a clyde.
Also, the chainstay breaking problem was in the previous year model (SISS). It was fixed for the SASS, haven't heard of anyone snapping one on the SASS's yet and it's been out for a couple years now. The rear wheel bearings aren't bad on the Spot hub, it just needs to be tweaked and loosened up a bit to reset the bearings so they wont bind. Check the Spot rear hub reviews for the lowdown. The headset is cheap, best to replace it, but push comes to shove it will last for more than a year if you keep it clean and lubricated (I still have mine after three years). The chainline was out, removing the bashring and moving the chainring to the outside cured the problem. I wore out the ISIS BB in about a month, your mileage may vary. Otherwise the SASS is a good bike at a good price, dig it.