I've been managing such a system for a little over a year, with no particular problems. Memory is indeed key, we're using 26 GB for SQL Server and 1.5 for QVS, but we could probably choke back SQL a little and fit within 24 GB without any trouble, if that's what we had. Our usage is pretty light, though, with only a couple people using each product frequently during the day.
We have eight cores, but CPU can still be pegged, but rarely for long. I have seen the QlikView distribution service use more CPU resource than I like; there's an open thread on the topic.
Of course, I'd make sure that your scheduled reloads in QlikView don't coincide with ETL, backups, scheduled reports, or other predictable resource-intensive tasks SQL tasks.