Alan,
In general, I have not had any significant problems with lay out tables.
Can't comment on the summary attribute.
There was one very specific instance where layout tables did create a
problem. My company has an expense claiming system. The screen looks like a
spread sheet. The page is a grid with a series of edit boxes laid out in a
table. Here, I had problems determining which column I was in while
entering the data.
Pranav