We decided to use FIAR this summer :-) The kids will be 5 and 6 soon and I want them to have a light summer, especially with my hip replacement in July. DS will continue to read, read, read and to review math facts 1-10 (addition and subtraction) and DD will stick with Phonics Museum and both will do Song School Latin (they LOVE it). I will lay out several weeks for my parents, probably 4, and I think it will work :-)
My kids loved FIAR when they were younger. I think that is an excellent summer choice. Keeps them reading and doing some fun activities through the summer. I can't remember the sites anymore, but there are some great resources to go along with FIAR, for free, online. A lot of Lapbooking ideas, printables, etc.