Problem is, there are many anecdotal reports of zRAM boosting system performance, but there is very little in the way of real-world benchmarks... (Michael? Might be a great idea for a future article). Furthermore, there is little consensus as to what the cutoff point is with regards to cpu speed/zRam usage to gain the best performance. Obviously, since zRam uses the CPU to compress memory, it will be faster on faster CPU's; however, does that mean it is a hindrance on slow netbook CPU's or mobile phones where available RAM is generally limited? It would be very interesting to see benchmarks on a whole range of systems utilizing zRam and compare them to similar systems w/o zRam.
About the benchmarks note that Linux 3.8 will also have a twice faster LZO compressor/decompressor module: http://git.kernel.org/?p=linux/kerne...1915e5ae057826 so numbers may even improve here.
It's not so much about performance, more about avoiding swapping (or running on systems you previously couldn't). I recall an early Ubuntu livecd test where the CD would crash before desktop on a 256mb ram machine, but with zram it could successfully install. (no swap in that case)
Since if you swap, performance goes to near zero ;)
zRam has just been enabled as an option in the Raspberry Pi kernel so it will be interesting to see what effect zRam has on these 256MB/512MB devices.