The card itself is very short so it should fit in just about any non-low-profile case. Likewise, the HeatSink/Fan (HSF) doesn't protrude into the next slot so there's plenty of room for other expansion cards. However, this does mean heat from the card isn't allowed to escape so your case will have to be well ventilated elsewhere to keep things cool.
When I first saw the cooler I was rather worried it would be pretty noisy as the tiny fan span itself silly trying to keep the card cool when under load. However, wrong I most certainly was proved. While it's by no means silent mid-gaming session, it is far from disturbing and is to all intents and purposes silent when idle or watching video.
Along the top edge are the two connectors for using the HD 4670 in CrossfireX. Just one connection is needed for two cards whereas the second connector is needed if you add a third card.
Simplifying things further is the HD 4670's power requirement. It also doesn't require any extra power connections as it draws all the power it needs from its PCI-E 2.0 slot. Essentially, so long as your computer's motherboard has an x16 PCIe-Express 2.0 slot you're good to go.
Our test sample provided by ATI came with an interesting output configuration. Rather than the conventional dual-DVI-I outputs, it has a DVI-I and two DisplayPort sockets. As well as giving you the ability to connect three displays to a single card the use of this new (soon to be standard) connection will be useful for when you do eventually upgrade you monitor. If you do still rock an old CRT monitor with a VGA connection, a DVI-to-VGA dongle on the single DVI-I output will sort you out.
Now the biggest contender for your money at this price point is nVidia's 9500GT. This card actually has almost identical components to nVidia's previous generation 8600GT so it seems performance is unlikely to blow anyone away. Nonetheless we've put one up for test so we'll see how it goes.