I have had and extensively used the 405, 110, and the 610. These days I use my 110 and 610. The 110 is quite bare bones basic, and use it mostly for races and as a backup. I would use it all the time but there are two features of the higher end Garmins that I really like: I like the ant+ wireless data transfer. It might not seem like a big selling point but once you get used to your data just magically appearing on your computer after a run, it's hard to go back to connecting cables.
The 610 feels quite heavy to me and it feels awkward on my wrist compared with the 110 and even the 405, so much so that I usually wear it with the display facing inward and higher up on my arm. The lug factor really is significant for me. For this reason, if I were to buy again I think I would get a 410.
I don't really use any of the features of the watch, except to record my runs, although I did get lost on trails once and didn't think to use "find my way back to start" feature which would have been useful.
If they made a really nice slim basic watch with just GPS and Ant+, and without the "training buddy", programmable workouts, and whatnot, I would totally get it. otherwise I recommend the 410.