The main problem for Mac users appears to be the older Java implementation:

Windows / Linux : JRE 1.4
Mac OSX : JRE 1.3.1
Mac OS 8.x/9.x : MRJ 2.2.5 (=JRE 1.1.8)

this, for example means no mouse-wheel support or Cut & Paste for Mac Users which is supported in JRE 1.4, I believe.

As far as crashes are concerned. Apart from increasing the memory, as Adam suggested, you can try deactivating extensions (OS8/9) as these systems tend to suffer a lot of crashes from extension conflicts especially when you have a lot of 3rd party (non Apple) extensions. I often use the Basic OS option in the Extension Manager which only loads some of Apple's standard extensions and no 3rd party ones. That generally reduces the number of crashes. If that fails, you can try restarting with no extensions at all by holding down the shift key at startup (Limewire should still run).