Well, this is a surprise. According to Mac|Life, the upcoming service pack for Mac OS X, dubbed 10.5.7, is due to be released on Friday. This is, as you can imagine, a rumor; Apple hasn't mentioned anything themselves, but apparently the source is within the company itself, so this could be credible.
Mac OS X 10.5.7 is due to bring a whole number of fixes and improvements, in areas such as "networking, syncing and BlueTooth issues," according to the website. OS X developers were seeded the most recent build, 9J58, on April the 29th. The build only fixed issues with iChat and Safari, so it's expected that this is the final. Additionally, it's implied that this will be the last update to the 10.5 iteration of the Mac operating system until Snow Leopard, which should have some announcements regarding its development at the WWDC in June.
Sit tight until Friday, Mac users, to see if this rumor pulls through, or watch it fall flat on its face.