I used OSB in my shop, EXTENSIVELY, also recently as well.
I have 3 bays worth (1 10' high, one 15' high), and 2 ceilings worth of it. I like it better than drywall for shops, it takes abuse that would leave drywall broken. On 3 of the bays I used drywall screws to attach it, they work well, but are a PIYA. On the more recent work I've used ring-shank framing nails from a framing nailer, that goes a LOT faster, and seems to be at least as secure, but watch your wiring.
As for paintability, there are two sides to this story, I'll give you my experience:
1) whatever you do, get a 1.25" nap roller, this is the only thing that will reasonably get into all the nooks and crannies in the board.
2) On OSB there is a rough side (made to keep people from slipping off roofs) and a smooth/glued side. When doing my first 2 bays I put the rough side out. It worked out very well and would reduce any flaking as previously mentioned. But it soaks up a LOT of paint. On my machine shop, I hung it all with the smooth side out. Takes less paint, will allow for smoother surface when complete and I think it looks better when done. I have never seen flaking like the previous poster showed. I suspect that the paint/moisture had something to do with it. Don't let the smooth side of the OSB get/stay too wet.
3) For paint I used a single coat of Kilz2 latex primer laid on fairly thick. Let that dry out for several days/week. Followed this up with 2 coats of Olympic exterior latex. Did this over 3-5 days and it's been pretty darned hot too, so it's been baking. On everything I have I used a high-gloss paint so that when it gets dirty, it will wipe right off.
4) Seams: caulk can hide a multitude of sins. I just went and got a case of that cheap/white/paintable DAP/Alex caulk. It works well. Hides all the imperfections in the joints, use it much like you would drywall mud. use it to hide nail/screw holes too.
If you look at my build thread you can see how everything came out in the previous stages, the original bays have been up for 1-2 years now with no trouble and no signs of trouble in the future.
As for cabinets/weight, towards the end of my build thread you can see how I did my Gladiator wall cabinets. I have almost 2 walls full of them. I wouldn't recommend hanging significant weight on the OSB itself. I like to over-build stuff just in case, so when we put them up, I put 2X6 runners up at the top/bottom of the cabinets, secured to studs with 3" deck screws. The each cabinet is hung with 4 each 2" lag screws/washers into the 2x6. In addition to the cabinets, this also gives a nice/heavy duty way to hold other stuff, like hanging hooks, etc.
couple pics: