When considering whether to purchase a 405 or 605, I was consistently bothered by the notion of how to record my favorite television shows (I work nights) and still be able to use my Archos at work to listen to music, etc. I couldn't understand why I should have to leave my unit behind to utilize the DVR function. Luckily, I found a great alternative to the DVR Dock.
If you have a 405 or the 4 GB 605, take a look at the Sandisk V-Mate. It works like a VCR only it records onto media cards (most notably, SD format cards) in an mp4 format. You can hook this thing up to any video source (analog/RCA connections) even a DVD player (it bypasses Macrovision encoding)!
Using its Medium Quality setting (320 X 240 resolution) it records almost 2 hours on a 1 GB card. I purchased two 2 GB cards (one for each night) and swap them in and out of my Archos. Now, I never miss a show and I always have my Archos with me. I still had to purchase the mp4 codec but $20 is nothing compared to the $100 Dock.