Of late the IM function of Skype seems to be flaky. Someone received an IM from me much later than when sent, and I got there reply at a time when I was on but they were't, yet it showed them online.
This morning it happened again. I've also noted some delays in authorization of users who add contacts to their Skype list. Even their dutiful PR person has not replied to an IM of mine from last week, and that's very unlike her.