I've been hard at work trying to tackle some lingering Leopard stability issues with Pukka and believe that I have a solution. I'm releasing this fix as a prerelease (i.e. not advertised in the auto-update mechanism and not posted to the download sites -- please do not post it for me!) since the problems don't affect everyone and I'd like to have some feedback from those who are affected before making this version live.
(You may note that I'm using the same link for both OS versions -- I'm just trying to get some rudimentary usage stats by separating out the download URLs ;-)
If you're interested in some more technical info, read on.
It seems that Leopard has some lingering crash issues when using NSURLConnection, particularly when behind a proxy and/or using HTTPS and/or using authentication. Of particular concern are the last two conditions, as all Pukka traffic through del.icio.us, Ma.gnolia, and most alternative sites is over HTTPS with authentication. I have rarely been able to reproduce these crashes myself (which is the main reason I did not catch them in prerelease versions of Leopard), but I have received crash logs from issues with severity ranging from occasional problems to repeated crashing, including crashing on launch. Needless to say, this has been very frustrating.
Any other Cocoa programmers who use NSURLConnection will note that it is pretty much the way to do asynchronous downloads to memory (i.e. not to a file as NSURLDownload does) while easily working with requirements such as the ability to cancel, authentication, transparent proxy support, and cache management. I've been in a bit of a bind for a workaround, but after some discussions with (extremely helpful!) fellow Mac developers such as Daniel Jalkut, Jon Wight, and Fraser Speirs, I've settled on the solution of using CURLHandle routines in a dynamically loaded bundle when on Leopard for the time being, linking them against a Leopard-targeted CURLHandle framework to bypass cross-development issues with the framework. This required a fair amount of re-architecting since CURLHandle is not intended to be a drop-in replacement for NSURLConnection (in fact, it's a subclass of the Tiger-deprecated NSURLHandle class). It's a stable and reliable fix for Leopard until this bug is resolved, if not super-ideal for me as a developer. But them's the breaks!
For the reference of the Cocoa developers reading this, you can check out some bookmarks I've gathered (and will continue to gather) about issues with NSURLConnection over the years here and I've reported the Apple Radar bug and it resolves to the original at rdar://problem/5575834.
Update: I just released 1.6.6-pre2 to fix an issue that a couple people have noticed with double encoding of text when posting. The links have been updated above.