I've had the OEM ones, and used them through more miles than I care to remember, I had them overloaded and they suffered a couple of 'off's' but still managed to complete 8000 miles around Europe without fault.
When I got back to blighty, I noticed a small stress fracture in one of the boxes (the one I fell against) and Yamaha replaced - I don't know how they did that, but they did and I didn't question it.
I did find them a litle on the small side to carry everything, and they wouldn't survive multiple falls - such as desert riding, or serious off road. They lack a rear stay, but for a mininal amount of cost and effort you could make something to do that job.
I never had any problems with the locks, I believe that people have problems because of poor PDI and poor maintenance, followed by a lack of respect for plastic fittings. Mine worked faultlessly.
However, I now have a set of Touratech Zega Pro's
These are not the kind of box you'd use for everyday use. They come in at the same width as the bars, so filtering is a bit hairy! They are however built to last, light and make comfortable seats!
The frame is a bit ugly when the boxes are off, but it does make for a very good rear 'crash bar', and is as strong as they come!
The inside of the mounting frame gives enough space to fit a couple of tool tubs for the really long range trips. Watch this space!
On balance, if you want to commute, and carry your books/files/laptop/lunch then the OEM ones are just the job, narrow, good looks, waterproof (to a point) easy to fit and remove, and the mounting frames don't upset the lines of the bike. If you want to do some serious travel - the OEM ones will do it, but you should consider something a little more robust, such as the SW or TT - Metal Mule have priced themselves out of the market on this though.