I've seen hardware RAID cards fail and take out an entire array. You are definitely adding another single point of failure with a hardware card, unless you're in a redundant configuration.
You should be aware that there's "hardware RAID" and then there's HARDWARE RAID. Google "fakeraid" for more info. Some "hardware RAID" cards actually do very little RAID processing in the card, and use custom drivers to do the RAID calculations in software, using the system's regular processor. This can lead to strange results. I had one of these system (a Windows 2003 server) start showing separate C and D drives, instead of one C drive, because something got confused somewhere. That should never be possible with a true hardware RAID, as it appears as one physical drive to the system.
I have very little experience with software RAID. I've been prejudiced strongly against it in the past, but am now moving towards using it, based on things I've heard here and elsewhere. I'd consider testing it for a future deployment.
On the other hand, I've moved away from any kind of in-server RAID to external RAID systems. Almost all my servers have zero drives installed. I'm in love with Xiotech systems, but other types of externals RAIDs have also served me well. I've never (knocking on wood) lost data from one yet.