Do you use bittorrent or some other file sharing service? From what I understand about the actiontec routers, VZN uses only a portion of the cache in the router. P2P programs can fill that cache quickly, choking the router. By restarting the router, you're clearing out the cache. If you are using a p2p client, try limiting the upload speed.
Also, is your network secure? Could someone else be mooching off your wireless bandwidth? Add a wpa2 password.
I have the same issue, like you I have the Actiontec MI424WR and everytime I attempt a (what I would consider a normal download) the device locks up and I have to reboot it. This has killed my online gaming and my ability to VPN into my office. Everytime I call tech support they say reboot the device and to top it off I'm on my 3rd replacement router. This might as well be a dial up connect, the only thing I can do is simple web surfing and viewing email. I switched from Comcast to Fios for the speed and it was cheaper but it's has turned out to be a bad move. Last time I called tech support I asked the guy if he knew of a work around his response was "No but we can send you a new router", I'm giving them 30 more days then it's back to Comcast.
I've had FIOS internet service for years without issue until I installed the new MI424WR router. I now have to reboot the darn thing all the time. I just signed up for the phone and TV service and am forced to use this new router which loses connectivity all the time when trying to download any files. The only solution is to reboot the router. I am now on my second version of this router and experiencing the same issue.
I am quickly losing confidence in this service and will switch if it is not resolved quickly.