All else being equal, is there any advantage or disadvantage to using 2 dimms of 2GB memory over 4 dimms of 1GB?  
 
Also, is there a tangible speed difference between, say, 4-4-4-12 and 5-5-5-15 timings?  
 
Keep in mind I'm not interested in gaming or benchmarks. I just need a fast, stable system. No OC'ing memory unless I can get a noticeable, real-world increase in performance.

Get 2 x 2 for sure. Some MOBOs have a little problem when you fill all 4 slots. And if you ever decide to get more RAM you'll be able to buy another 2 x 2 set to get to 8 gig.
 
The timing difference is not much on current Intel systems so don't pay much extra for the 4-4-4-12.

both 2x2gb and 4x1gb are good, if u want to upgrade your RAM soon then go for 2x2gb if not go for 4x1gb, many say that 4x1gb doesnt OC good or its hard to OC it but its not true for 100%, i am one of the happiest 4x1gb users
 
also 4-4-4-12 is better than 5-5-5-15 timings and i recommend u getting  
a RAM with 4-4-4-x or lower timings

Go for 2x2GB. You'll leave 2 slots for future expansion, possibly achieve slightly higher OC's, and avoid any potential issues you could have with your board.

Take 2x2GB

2x2 for overclocking and upgradability
1x4 for CAS and lower price

 
It's better to buy 2x2, but you have to be careful. Some "cheaper" mobos have problems with 2GB

 
I'll second that one

 
Agreed.
 
4 x 1GB takes a little more tweaking, but go for it if you are willing to save some $$ and take up a challenge.  For my light OC, the chipset required more voltage (NB and VTT) compared to 2 x 1GB.

Go with 2*2GB. This gives you more open RAM slots for future upgrades.

I haven't been able to find any 2x2gb sets that come as pc2-8500 1066, only ddr-800 seems to come in 2gb sticks.  I agree that 2x2 is ideal, but is it worth the hit from 1066 to 800.  Keep in mind this is for a new system next month or so with a Q9450 and nvidia 9 series if they do happen to release soon.
 
thanks.

i believe OCZ offer 2x2gb pc2-8000 1000mhz if thats any good to ya? ReaperX seris

Just make sure it has micron chips
http://ramlist.ath.cx/ddr2/

 
Areyou responding to the previous post, or is that a general rule?
 
The RAM I was gonna get (G.Skill 2x2GB F2-6400CL5D-4GBPQ) has "Powerchip" listed. Is this OK to get?

Sorry, just saw you don't want to OC.
 
Yes, they'll be OK for what you want them for - to run at their rated speed.  They don't have as much OC headroom as micron based chips.  If you find 2 x 2GB with micron at a similar price, I would get those.