I bought my 642 because it was a new return - and the store had it marked the same as a few really used 642s, varying from used to beater condition - $315 2/07. Locally, a shop had 442s for $409 - I nearly bought one the day before. The owner took $315 OTD, possibly because of the IL (Mine is a 642-2.). I had been carrying my 296 in a Mikas pocket holster - and I had ordered a 642-sized one at the same time, so when I got home, I was elated to find that the smaller sized 642 fit my pants pockets that revealled the 296 - it could see 100% carry! I hated spending my gun-money on a SD device - it would sure go a long way towards another plinker. Sadly, a SD piece is a 'must have'.
About the IL... the company that bought and still owns S&W is 'American Safe-T Lock'. They have been putting the infamous 'IL' in most every revolver they've made over the last nearly six years. I've bought nine so equipped over that time - and only sold one, a 4" 625 I replaced with a 625JM. I own/have owned fewer without it, actually. I have never had a problem. Oh, I tried... shooting with the lock half engaged - with/without the key, etc. It always ended up 'off'. Just a guess, but I bet they really tested it before offering it. No, I wouldn't specify an IL in any of my firearms - I wish I could save the cost of a trigger lock and plastic box, too. But, I am a realist... the 'IL' was an attempt to stay marketable in all fifty states - as was the fired case inclusion.
The most prone to failure part in the IL is the spring - which, like all spring steel, can rust - and fail. It's ability to hold the lock in detent can also be tested by sudden and violent movement. This can come about by impacting a hard surface after enjoying the acceleration due to gravity - or simply limp-wristing the revolver during recoil, highly likely with a 329PD and some hot .44 Magnums. We can agree that dropping a revolver isn't likely to have a great outcome anyway, IL or not. Also, the extra movement in recoil can accentuate the release of a heavy bullet from it's crimp, the reason my 296 is limited to 200gr maximum, and that really locks up a cylinder. The probability of a spontaneous IL failure is orders of magnitude less than the probability of a bad commercial round. Using some folks rationale about not buying an IL-equipped S&W, they shouldn't put ammo in it, either - it's more likely not to work, anyway!
So... if I didn't have my 642, and money wasn't a problem, I'd likely get a 442 - maybe even a CT grip - and never worry about the IL. YMMV.
Stainz