I agree it is very hard to stay focused in the summertime while at work. What helps me is to try and get as much work done as I can in the morning before lunch. That is when I feel I am most productive. Then I make sure I unwind during my lunch break. After lunch however is the hardest part of the day for me. I have found recently that plugging my headphones into my ipod and listening to music in the afternoon has been really helpful in keeping me focused. I also make sure I pack an afternoon snack which gives me a little energy boost during the afternoon when I start to get a little drowsy.