Using the first language in the second language classroom

Next autumn (2011) we will get new syllabuses here in Sweden and today I had a look at the proposal and in there it was written: "Undervisningen ska i allt väsentligt bedrivas på engelska". This wording is not to be found in the present syllabuses.
When looking for a research article to discuss in our group my choice was "First language and target language in the foreign language classroom" by William Littlewood and Baohua Yu. The authors discuss the balance between using the target language and the students' first language in the second language classroom.
For many students the classroom is the only opportunity they have of using the target language. It has therefore for quite some time been considered that the target language should be used as much as possible in the classroom and the first language should more or less be avoided.
But when the authors asked a number of students about the use of the first language in the foreign classroom it turned out that even though the teachers agreed that the target language should be used as much as possible, there were situations when they tended to use the first language instead. These situations were mainly:

• when establishing constructive social relationships
• communicating complex meanings to ensure understanding and/or save time ('explaining difficult grammar' or 'giving the meaning of unknown words')
• maintaining control over the classroom environment
  (p. 5)

The authors argue that there are situations when using the first language can be motivated, for example when contrasting the two languages to understand certain grammar points or when clarifying the meanings of words structures and utterances. However, the goal should be to use the target language as much as possible and this may now, as seen, be stated in the Swedish syllabuses and I agree with this, and so do my students.
But there are situations when I prefer Swedish and that is for example when talking about grammar since I think it can be confusing enough without having to learn the terms in English as well. Then there are days when I realize at the end of the lesson that we have spoken a lot of Swedish and I can't really say why.
What is your opinion about using the first language in the second/foreign language classroom?