F5 http file download failover?

If you are referring to an induced/voluntary failover (you instruct the Active unit to become Standby) you can using connection mirroring for the virtual server to make the failover completely transparent. F5 doesn't recommend this, though, for http due to the overhead involved and the generally forgiving nature of http. Unless F5 changes have been made recently, the transparent failover doesn't work when you've got ssl profiles attached. In general, from an end-user perspective, failovers when http is involved are pretty seamless.