Reserved my Wii at 10 AM today after getting there at 7:30 to be 2nd in line.
Only 11 people actually got to reserve Wiis (I'd say 15-20 others were turned away). Will they likely have more on launch day? Yeah, sure, but I don't see the harm in nailing it down.
My GS will be doing a midnight Wii launch and I asked and ensured that, at midnight, they will have a bag of prepaid merchandise waiting for me (all I need to do is add an S-video cable and I'm set): Wii, 4 controllers with chucks, Red Steel, THDJ and Excite Truck (a roommate will be getting Zelda).
I walk in, no "line", they hand me my sh*t, I buy the cable and I'm on my way home (which is closer to GS than it is to Wal-Mart).
Now, I don't TRULY believe that there will be an issue in supply. HOWEVER, consider the amount of press and mainstream attention Nintendo is already receiving and they haven't even officially started running TV advertisements yet (at least not that I've seen). If 30 people show up at 10 AM to preorder a Wii in a sh*thole region of NH (a sh*thole state, FYI) with no formal advertising campaign being launched, then clearly Nintendo has done something right this time around.
When I bought my GC on launch day, it was me and my friend waiting outside GS in the mall, the only GS in 30 miles, and we were the ONLY two there to get our cubes, and this is after Nintendo had already begun its formal advertising.
This time, Nintendo has people rushing to preorder despite the fact that they've made no REAL drive to get the Wii into the mainstream public eye. 20+ people at this Gamestop which is new and hasn't been around more than 2-3 months and there are 2 other GSes and an EB in driving distance which people could just as easily have preordered at.
I would NOT use the Gamecube launch as a guideline regarding how the Wii launch will pan out: everything is already moving MUCH faster than anticipated for the Wii (despite similar warnings about shortages from the GS newsletter, the PS3 didn't have this many people lining up for it).
I expect to see even more increase in demand for this thing once Nintendo rolls out its actual ad campaign and I wouldn't be at ALL surprised if it gets pushed into "Furby" or "Tickle Me Elmo" status this xmas.
My advice: better safe than sorry.
Even if the Wii doesn't skyrocket in popularity, I'll still have it in a convenient bag I can immediately walk out with and little to no line to worry about and that's worth preordering in my mind anyway.
That said, I'm sure you'll get one during Nov, even if the launch shipment sells out.