is bitcoind reliable when depending on it for web services? What I mean by the title is, say If I create a service with bitcoind being used to create and store large numbers of accounts and address, is it likely to take the strain? Can I setup multiple instances of bitcoind to access information about the network or would I need to one large instance of a bitcoin daemon to handle everything?

If not is there an alternative to be used that can keep up with an expanding web service?
I think bitcoind is perfectly suitable for it, if you can securely access it via RPC.

You can easily create a separate bitcoind instance when you experience that only one instance cannot handle the load, but keep in mind that a bitcoind instance can only send coins it has the private key from, so you will have to separate all your queries into two parts, one for every instance.