They're a company to take seriously
We've run our business on 40TB of their storage for the past couple of years, NAS flavour. The hardware's bombproof: we haven't had so much as a spindle fail, such is the love they wrap them in within the Bricks, and the electronics have been noticeable only insofar as we haven't noticed them. The volume management and QoS is likewise invisible `just works' stuff, and I'd extrapolate from our NAS experience to say the SAN products are probably plug in, beat with a massive workload and forget.
The NAS product is a lightening-fast NFS server, but obviously has a much larger software stack covering filesystems and the upper-layer protocols. The NFS works perfectly, and hasn't crossed our radar since day one, and the filesystem performance, snapshotting and the like all does what you'd expect.
We've spent a bit of time chasing around a couple of NLM issues, but that's a protocol that suffers from poor specification and our environment --- interworking between Solaris and Linux clients --- has a history of stressing even the native Solaris implementations on past Suns and Auspexes (Auspex never `deep ported' lockd, instead running it on the Solaris host processor at hideously slow speeds). The Pillar version is running on the slammers and has performance and resilience to spare, but has some corner cases where it behaves differently to the reference implementations. But the fixes have usually been rapid, and it's not really got in the way of production loads. We're supporting multiple Solaris Oracle platforms (primarily a couple of Niagaras) off it, plus 1000 users of Cyrus IMAP, home directories for those 1000 users, a 200-user Clearcase environment, and it's barely raising a sweat.
I'd be lying if I said it was trouble-free, because nothing is and we're at the right-hand end of the complexity curve amongst their customers. But of the new products we've brought into our network it's been one of the easiest. And when we have had issues, the company is one of the most customer-focussed we've dealt with, with top-quality people at the end of the phone directly and short, effective escalation routes. The management team are straight-forward and decent and the price / performance is great. If you're shopping for storage, they're well worth looking at.