1) Capacity is mentioned in decimal sizes by hard drive manufacturers in order to up the apparent spec without adding additional cost.
Operating Systems count sizes in binary amounts, 1000 bytes is of no use in a binary counting system, whereas 1024 is much easier to use in binary. 1KB = 2^10 or 1,024 bytes, 1MB = 2^20 or 1,048,576 bytes, 1GB = 2^30 or 1,073,741,824, 1TB = 2^40 or 1,099,511,627,776 bytes, and finally 1.5GB in binary is 2^40 + 2^39 or 1,649,267,441,664 bytes, which when abbreviated into human readable form looks like 1,649GB or 1.6TB for short. Of course, HDD manufacturers should use the binary capacities as the listed capacities but they don't since selling to chavs always reduces to the lowest common denominator of understanding. They use the decimal capacity since it looks like you get more for your money.
2) Reliability is a factor of many things. Quoting the MTBF of hardware is (for me) useless since WTF does 1,200,000 hours mean time to failure mean??? Come on, that's like 120 years! As if! Reliability can in no way shape or form be predicted accurately for an individual component much less an individual drive. Over the years (I bought my first HDD in 1986) I've had varying degrees of success with Western Digital, Seagate, Maxtor, Samsung, Hitachi, Connor, IBM, Quantum, and the god-awful Fujitsu. I can honestly say by far the most important item for maintaining a reliable drive is to make sure it never runs hot. If it does, it WILL fail, and usually pretty quickly. If a standard desktop drive runs in a 20°C ambient environment, is kept stable, and not subjected to undue physical stress, it will last (and I have drives to prove it, from various manufacturers) at least 5 to 8 years if not substantially longer. Just for your edification all drives I currently use are never turned off, they run without power management 24x7x365. Perhaps the absence of in-rush current stress is giving me a better experience. Also, I best mention I will probably now suffer a bunch of sudden failures simply because I wrote this comment.
As an aside, I can't wait for SSDs to become mainstream since that will seriously increase reliability, performance, power efficiency and will reduce noise pollution (ever heard an SSD? I thought not).