Auto-upgrading from 1.4.3.1 to the 1.4.4 or 1.4.4.1/2 versions did not work for me. Sparkle's error handling was unhelpful and just backed out of the process. I eventually installed a fresh 1.4.4.2 to work around this.

The console output was similarly unhelpful in identifying the root cause:
6/14/12 1:04:00 PM [0x0-0x1c61c6].com.torusknot.SourceTreeNotMAS[8457] "disk5" unmounted.
6/14/12 1:04:00 PM [0x0-0x1c61c6].com.torusknot.SourceTreeNotMAS[8457] "disk5" ejected.
6/14/12 1:04:01 PM SourceTree[8457] Sparkle Error: An error occurred while extracting the archive. Please try again later.

Earlier Sparkle upgrades had worked smoothly.