I have to throw my 2 cents in here. I now have 5 raspi's, and bought 5 different cases for them.
1st one to arrive was the Adafruit case like yours. And in later days and weeks I got a Lego, Built-to-spec, Pibow and modmypi cases.
The pricing of all these cases was around 30-35 NZ dollars landed, close enough for the price differences to be negligible.
The quickest to be delivered was the adafruit, then built-to-spec, then Lego, Pibow and slowest was modmypi.
The best case would have to be the pibow, the fit of the raspi is bang-on, and nothing moves a millimetre once assembled. Its small, solid and looks the part too.
Built-to-spec (BTS) has the next best case - its a close thing between it and the pibow. The BTS has been well designed, I like the 'industrial' look.. but the case does move a little when you twist it... and the raspi isn't held firmly inside, there is about 1mm of up/down movement on the SD card end.
Next, in my opinion would be the modmypi case. Its a very simple clip together affair made of thin light (cheap?) plastic. There is more movement of the raspi, but I used a few bits of blutack to keep in under control. It looks tidy enough, although the price is about twice what I would expect to pay for such a unit - its 2 parts, and manufactured using injection moulding (I would assume) or similar.
Compare the complication of this to the BTS case that has maybe 20 separate parts? for essentially the same landed price. Manufactured cost of the modmypi should well under $1 (60p) - in a perfect world with MASS production etc. (Delivery was also the slowest - by some margin).
Next best case is the LEGO from The Daily Brick. Made of perhaps 60 lego pieces it's...... well it's LEGO - quality assured. But the inventory of LEGO blocks is obviously limited and this case suffers from that. Lateral movement is held in check as the blocks sit snugly up to the sides of the raspi board, but there is nothing within the LEGO case to prevent up/down movement, and so the board does move around significantly. This can be somewhat remedied with (a big wad of) blutack again... but it would be nice to have a better method to prevent the movement.
In a distant last comes the Adafruit case. It is a simple enough design of six separate pieces that are held together with flexible 'clips' that are incorporated into the side panels. The acrylic is clear, and so it shows off the Raspberry Pi nicely, but the design is a let down. Once assembled there is significant torsional flex in the case when you apply a twisting movement, and the whole unit rattles as the panels are only held together by the flexible tabs (clips) on the side panel. On my particular unit one of these panels was warped (a substantial bow in it), and so this did not help the rigidity.
If you dropped this case it WILL (most likely) fall apart into its individual components and possibly break.
When I dismantled the case to retrieve the Raspberry Pi, one of the tabs (or clips) broke away from the (warped) side panel and so now one end of the case is only held on by one clip. The case was fragile before, now even moreso.
That is my quick and dirty roundup of some of the more popular Raspi cases.
In conclusion, I would recommend a pibow, although it would be nice to have a variation of available colours. 100% clear acrylic would be a good option. But you cannot get a more solid, compact, well fitting case in the small range of cases I have tested.
The BTS case is well worth considering if your like the look (I do), It is solid with little flex, but the Raspi does have a bit too much up/down movement. It seems the builders are considering selling a clear case alongside the current black and purple.
The Built-to-Spec case has been well thought out with only a couple of design niggles.
I do NOT recommend Adafruit unless you MUST have a 100% clear acrylic case. It looks good, but the attraction stops there. Too bad that.