Sizing and striping log area

Forgive my ignorance, but what should I consider when sizing the partition
which houses the pg_xlog area? Are logs cleared out every once in awhile
or do they continue to accumulate? Let's say your DB is around 4 GB,
what should the log area size be, or does the size of the DB not matter,
if not which factors should be considered?

Also, on a related note, would putting the pg_xlog onto a RAID-0 array
improve performance much? Striping seems great for parallelizing seeks,
and seeks are, if I recall, the main bottleneck for disks. But since the
logs are written in a serial manner, there should be little to no seeking so
performance gains wouldn't be all that much compared to dedicated
single disk logs?

Now straying even further from the original subject... Would hardware vs
software RAID 0 not make a difference in reality? Software striping
incurs CPU and SCSI bandwith overhead. But in production CPU
shouldn't in theory be more than around 50% or so, if so there's a
capacity issue and you should consider upgrading CPU. And with
most modern SCSI cards, bandwith is much greater than disk
speed, so the extra overhead wouldn't make much difference. This
might explain the popularity of Veritas.