I am also having this issue. I have a new-ish 27" iMac with 8GB of RAM and a 1TB hard drive. I have 690GB free on that drive. I am still getting these errors from time-to-time. It's a little concerning, but I really want to figure out what's at the root of this so that I can avoid it in the future.
My biggest issue is that - if we're talking about the swap file here - I have 690GB free. No swap file on earth should get that large. It's not like I'm editing all of NASA's imagery at the same time. I do have Parallels running, and I am taxing my system. My physical ram (again, 8GB) is frequently maxed out. I just can't imagine why the swap space would be insufficient. I've only noticed this since 10.6.6, BUT my usage patterns also changed around that same time. I am now running more memory-intensive apps in both Parallels and OS X.
Any help?
Model Name: iMac
Model Identifier: iMac11,1
Processor Name: Intel Core i7
Processor Speed: 2.8 GHz
Number Of Processors: 1
Total Number Of Cores: 4
L2 Cache (per core): 256 KB
L3 Cache: 8 MB
Memory: 8 GB
Processor Interconnect Speed: 4.8 GT/s
Boot ROM Version: IM111.0034.B02
SMC Version (system): 1.54f36
Macintosh HD:
Capacity: 999.86 GB (999,860,912,128 bytes)
Available: 689.25 GB (689,246,728,192 bytes)
Writable: Yes
File System: Journaled HFS+
BSD Name: disk0s2
Mount Point: /