yes, I know of 2 friend who's main income was from selling on ebay. it got to a point where they had to have a small warehouse, a couple of employees to keep up with shipping, answering customers emails and order processing.
some draw backs include:
You have to figure out and stick to a strict posting schedule to make sure you always have all of your products on there.
pretty hefty bill from ebay at the frequency they're selling and posting on ebay. his monthly bill from ebay was always in 5 figures.
and yes, without employees, (if you're selling stuff out of your garage ) No non-working vacations.