I run the picaxe programming editor on windows XP in a virtual machine (parallels desktop) on my OS X laptop. The serial connection to the picaxe 28x1 works fine when I'm just communicating using hyperterm or when the picaxe sends debug info.
When I want to upload a program to the chip, it usually takes 4 or 5 tries to get it right. The larger the program, the more it fails to load.
So i decided to use the command line compiler for mac OS X. Now the uploads are very stable only a new problem appeared.