It shows up as memory use in the KDE system use widget, which showed around 80% of my 2GB memory in use around a week ago. Then I started a virtual machine that demanded 512 MB memory, and around 500 MB was transferred to swap. As I started and stopped heavy memory applications swap grew to around 680 MB by this morning, and RAM use was also around 70% with one VM (384 MB), Firefox and Kmail as the only applications running.
I use Ctrl+Esc and clicked to order processes by memory, and there it was - irqbalance hogging 275 MB. I restarted the service and the use dropped to 20 MB and swap emptied completely. My machine had been up 15 days so that averaged a leak of 955 MB/15 or nearly 60 MB/day.
There is a note on the memory leak patch submitted in November that it only applies to running irqbalance as a command and not to daemon mode, which will be patched at an unspecified later date. So until that is done we are stuck with the leak.
A daily restart seems the best workaround I can think of to keep it in check. Of course that will happen automatically to most users who shut their machine down when not in use. Only those who run it continuously need worry.