it's all about how good the support is. we resell hosting, but it's not really something we're bothered about making money from, just a convenience thing so that we have full access to client hosting accounts, and can upgrade them etc. as and when.
Generally when everything is running, there's nothing to do but send out invoices when you need to, or make backups for them, BUT.. when things go wrong, you better make sure that your hosting reseller account people move pretty damn quickly, because as far as your clients are concerned the buck stops with you.
I've been pretty lucky, I use
www.hostingmatters.com and whenever there has been a problem (which of course will happen - computers go down, hosts get attacked, etc. we all know that), they have moved pretty sharpish, and have numerous resources and ways to contact them that aren't tied to thier own servers.