Correct me if I'm wrong, but p2pool is a pool, not solo mining. What am I missing?
It is however what is the advantage of solo mining?
Helps to keep bitcoin decentralized?
p2pool is just as decentralized you do your own work and your own block headers.
p2pool has no fees. Actually right now members pay a BONUS to miners so think of it as negative fees.
you can merge mine w/ p2pool (alt-chains aren't pooled)
p2pool is equally DDOS proof.
None. If p2pool network ever went down you could always switch to solo or a backup pool.
One thing to keep in mind is that although current difficulty requires ~1.3 million shares per block. 5 millions shares isn't that unsuual and sometimes pools hit 10 million shares.
To put that into perspective if you got unlucky and it took your 5 million shares to solve a block at 3.5GH/s that would take ~70 days. If it took 10 million shares it would take you 180 days. Of course during that 180 days you would earn nothing, rack up electrical bills and continually wonder if you have something configured wrong.
Still if you absolutely MUST solo mine then I would recommend running a bitcoind on another machine to acts as a backup instance or use a pool as a failover. Currently if your bitcoind crashes on 1 machine your entire farm goes down for however long it takes you to notice and fix. It creates a single point of failure.