It seems that yesterday's appearance of the iTunes Match service in iTunes was a little premature. Not long after posting, the option seemed to disappear from iTunes account information, while those charged had their money refunded. Luckily, the option is now back, and appears to be in full working order.
It still costs $35 a year, still uploads library information and missing tracks to the cloud and still only has a 25,000 song/10 device limit. But it appears to be working, and that's a start.
Anyone played with it yet? What are your thoughts?