Please enlighten us all...
In order to be valid, a community design must be new, and of individual character. Novelty means that no identical design (different only in immaterial details) has been made available before the effective priority date of the filing.
A design has individual character if the overall impression it creates on the informed user is different from any other design that has been made available to the public.
When it comes to registration, there is no substantive examination to determine whether the design registration is valid. Examination is only for formalities like checking that the application form has been filled in properly. It's open to companies to check out what designs have been registered, and then they can apply to invalidate at any time.
For the purpose of a community design, disclosure is not deemed to have taken place if it could not reasonably have become known to the circles specialising in the sector concerned within the community. This limits the effect of very obscure designs, but the sector concerned is that of the alleged prior art, so its effect is more limited than it might at first appear.
A community design is infringed by any other design that creates the same overall impression on the informed user. Questions of whether copying took place are not relevant - copying is not a requirement for infringement, nor is it sufficient to determine infringement.
The scope of protection is not limited to a particular class or application, and is determined by the representation of the design as filed in the application. In the case of the Community Design Registration (CDR) that Apple used to get an injunction against Samsung, the scope of protection is not determined by considering whether a Galaxy tab creates the same impression as an iPad, but whether it creates the same impression as the design as shown in the representation filed. Since the Apple design representation is a line drawing, questions of colour and material are not relevant.
Features that are solely dictated by technical function are excluded from protection. This is interpreted in the sense of requiring that functionality is the only factor in the design of the feature (i.e. aesthetics being irrelevant).
In practice, recent cases before the UK community design courts appear to have shown that the bar is pretty high for infringement, and designs that were clearly "inspired" by striking designs which are protected by design registration have been held not to infringe. The informed user is not the average consumer, and to create the same overall impression is quite a high bar (see Dyson v Vax EWCA 2011 & EWHC 2010 for a recent example
http://www.bailii.org/ew/cases/EWCA/Civ/2011/1206.html www.bailii.org/ew/cases/EWHC/Patents/2010/1923.html)
I've not read up that carefully on the Apple v Samsung CDR dispute, but I understand that it has not reached judgement, but that an interim injunction has been sought and obtained. In the UK, this requires only that there is an arguable case, that damages are not an adequate remedy, and that the balance of convenience to the parties is in favour of granting the injunction (i.e. more or less that appears to be the most fair course of action).