Apps considered good Mac apps typically use native GUI or polished custom GUIs that fit the aesthetic and conventions. Multi-platform stuff like Eclipse and MonoDevelop are slapdash in that department.
Eclipse is one of the best java editing environments though, in terms of understanding java and not just editing text. Yes it's fidgety and ram hungry, but using it is a significant improvement over vim etc strictly in terms of my productivity. Though it may only really demonstrate value on larger apis; if you can keep most of an api in your head, ie it's a very small java project using few external libs, it may not do much for you.
And I just bought 16GB of ram for my macbook for $150; it's from crucial which I've had good experiences with but it's as expensive as it gets for 2x8GB. So that's a pretty trivial expense for your development environment: $75 a year.
You and the OP are comparing apples and oranges. VIM is an editor, Eclipse is an IDE. You can have your cake and eat it too [1]. Eclipse is a good cross platform IDE yes, but throwing more RAM at it won't make it feel natural and native to the platform.
Is there some sort of secret to getting Eclipse to work without being really slow? Someone once mentioned using the latest Java, but I've yet to give that a try. Frankly it's the only thing that demotivates me from writing Android apps.
Whether something 'runs' vs whether it's 'slow' are entirely different matters. Eclipse still hangs and stutters while using it with generally nothing else of substance running on the machine. It's better under linux than osx, but it's still there. Intellij has far fewer of these hangs/pauses, although it has some too. Looking fwd to java 1.7 to help reduce these issues.
