Sleep in it? May as well wear it!
According to this Wall Street Journal story, high thread counts are coming to a shirt near you just as you were getting used to sleeping in your Frette sheets:
In an effort to justify higher prices, high-end retailers have started selling men's cotton shirts with thread-counts as high as 220. On a typical men's shirt, thread-counts, which measure the number of threads per square inch, are about 100 or less, retailers say. Generally, the higher the thread-count, the softer and lighter the shirt.
[For example, this] month, Thomas Pink introduced a line of $325 "200s" cotton shirts for men (with a thread-count of 200) in blue, lilac, white or pink with stripes or checks (call 212-838-1928 to order). It also has custom-ordered, 200-thread-count shirts for $425.