Just a little one today - at 8x10 inches. Recently I have been thinking quite a lot about scale and I have decided that I will mainly work at a maximum of life size - it just seems to work better for me, rather than the big heads popular at places like the BP portrait award.
Partly this is because that although I do work in (many) layers, what you see (especially skin) is generally done in one go - and that gets difficult beyond a certain size.
The paintings done in the life room are also "one-go" paintings and don't seem to work if any edge is longer than 12 inches. I suspect this will hold true of painting plein air too.
So currently I am investigating supports - how to get good, small surfaces in various proportions - and this seems much harder than you'd think, with most manufacturers producing a very limited range. However, I have found a source of small stretcher bars and am working on stretching and preparing my own small canvases. Boy does oil primer stink!