Just to give 2 cents to the comments about speed or performance issues with eclipse/netbeans:
The only part of an IDE that sucks if it is slow is the editor component.
And in contrast to some obviously superficial assertions here, I found the editor
component in Eclipse extremely snappy. The rest of the IDE is prone to lags,
but the editor itself delivers spotless performance.
I have a 1.4GHz Laptop and use Eclipse with it. Eclipse's editor component is faster (especially when scrolling/browsing through text) than Code::Blocks or KDevelop. The simple reason for this is: Eclipse caches everything, especially the syntax highlighting etc., other IDEs seem to try to do this ''live'' and fail.
The c++ indexer was a cause of woe in versions past. It crashed when out of memory, without it none of the nifty search functions worked, etc.
For the current version I can only say: It is all fixed and it works like a charm.
It's speed is comparable to the VisualStudio Indexer.
If you install Eclipse CDT you get a ton of nice features as has been explained in other replies already, that most other IDEs only provide with multiple plugins. (I don't know about netbeans, never used it.)
The feature that kicks me everytime is the smart tooltip when I hover over some identifier. Eclipse gives me direct access to any javadoc that might be entered somewhere and the file where it is defined and even lets me scroll around inside the tooltip!
So I have every identifiers full context at my fingertips, everywhere.
I prefer it over Visual Studio and pretty much everything else I've tried.
Granted, everything else you do in the IDE could be snappier. For me, the crucial thing is, that the editor is fast and eclipse's definitely does a great job there.