Well, it depends on which bulbs you go for.
The T5 HO bulbs are quite strong (picture 2 below). The fixture is a SunBlaze 2 foot, 4 bulb fixture with 4x 6500K lights. I use these for cacti. Cacti that are about 2"-6" tall, I keep the light about 10"-12" above the plants. I've definitely sunburned small cacti with T5 HO lights. The big guys you can put about 6", or less, from the lights without problem. For low-light tropicals, I put them at the outer reaches of this fixture when I need to, though I prefer to put them under regular flourous.
I use a single T8 4100K, 3-foot bulb for the "tropicals" and keep the light about 2" to 6" above the crowns (picture 1). Sometimes one of em gets taller and sits right below the light, not even 1" away and they still do fine.
Also, for total number of plants, you'll be much better off with the big T5 HO fixture and do what New Wisdom does. From what I remember, he has stepped tables below his main light. That way plants that need more light sit very close and plants that need less can sit near ground level.
Also, for nice way to get a grow light into a house without a big disturbance, you could use a cabinet of some sort (pictures 2 & 3). Armoires work well and so do entertainment centers. I prefer entertainment centers because you get all sorts of nifty drawers and such to store seeds, ferts, ect.
Hcc