Nobody's gonna argue with me? Damn do I swing that much weight around here (OK NO FAT JOKES!)?
Ok, let me explain further my reasoning why a sub 10g nano might be better than a 50g SW tank for a newbie.
Firstly lets look at cost, I think my 2.5 with all the gadgets bells and whistles cost me less than a 50-55g tank and stand. That includes livestock and stand - thus if there was ever a major crash - honestly *ALL* I'd probably just dump the contents and start over. A major crash in a 50g tank - could result in needing to replace 500+$ alone in live rock.
Secondly, in a very small nano you notice all the little creatures. Not just the 'showpiece' fish. I can ID various copepod and amphipods now that I've owned this 2.5. Because those little critters cruising the sand become more noticeable in a tank this size - thus you're more likely to notice quickly when some parameter goes on the decline... With fewer things to look at you have fewer distractions - and have to pay more attention to what is in the tank.
You learn more about husbandry in a small tank, you're less worried about fiddling with the (non existant) skimmer etc or other hardware. More worried about overall condition of the tank - and you're quickly trained that the solution to every problem is a water change (And those water changes aren't going to set you back 30$ or more just in salt mix). Additives are little worry - cheaper and easier to do a water change than buy XYZ "Super duper reef chemical", a good habit to get into - I know many tanks that have crashed because some dummy added too much iodine, molybdenum, kalk, strontium the list goes on and on and on...
Because you're dealing with such a small volume of water, you tend to make sure you're getting the best test kits, a refractometer (hydrometers are hard to use in a tank as tall as the damn hydrometer). Setting yourself up for better success in the long run.
While the "Bigger is better" is probably a good motto for stores - since they get to sell you all the "Crap" you "Need" to keep your tank running, is it really true? Yes I can't exactly leave my tank unsupervised for a week at a time - which might not be a problem with a 180g tank, but who really needs that ability? And if they need that ability - should they really be getting into reefs?
Andy