I recompiled everything with GTK+ 2.6.10-r1, which has Cairo as an optional feature, and now aMule has been stable for 24 hours. Cairo still needs to be compiled as a dependancy for Pango, but apparently isn't used (by wxGTK?). For GTK+ 2.8 series Cairo is required.
phoenix:
Sorry, can't remember crash reason and I forgot to log it. I'll post info about Cairo problems on Gentoo 64-bit if I find any.