I have just taken official Sitecore Developer Training and Certification in their office in London, near Tower Bridge.
In general, I did not expect the course to be so intensive. 4 days going through all aspects of working with Sitecore filled many gaps in my knowledge of platform. There were 5 of us so everyone could receive proper support and explanation while stuck with anything while studying.
Thanks to our tutor, Raul, who has heroically stood out a flurry of questions from me and gave really great insights on quite advanced topic outside of course agenda.
My advice for those who are just about to sign up for it - treat this course not as a final result by itself, but as a starting point for your individual further investigation. You will not become an expert after getting a certification, but you will be aware of most Sitecore features you need to know at that moment and how they function. Thus, do the notes, as much notes as you can. And ask as much question as you feel important to satisfy your understanding of each exact feature.
Another point I would suggest is to postpone your training if you are complete newbie in Sitecore. In that case, there is a risk you may miss something very important, especially if that becomes a prerequisite for further module. Do your own research before attending the course as much as possible - read multiple blogs, Q&A on StackOverflow etc. and ideally form the list of your own questions that you'd find answers for, while taking the course.
I personally found that very useful, so do recommend to you guys. And yes, if you are successful enough, you shortly receive a certificate like the one below but with your name, and also gain access to Sitecore developers' resources such as SDN forums and support.