It's a matter of choice.
GPUs won't last more than 2 years mining, beacuse you'll fry them. Best to do is mine 6-12 months and resell them.
ASICs are more efficient in terms of power draw, so you get your ROI sooner, that's all.
Yes, scrypt ASICs won't mine scrypt variants for now (E.G. Vertcoin).
Scrypt multipools are fine with ASICs.
AFAIK GUIminer won't work.
I'm not so sure about the 2 years. If they're gonna break, it'll probably be in the 1 year warranty period, and don't a lot of them have a 3 year manufacturer warranty too? The only one I broke was only 2 months, and that got excessive dust on the little capacitors and they exploded. I think that was bad design anyway because later ones had much bigger capacitors there.
Yes the power cost is ridiculous with GPUs, that's the reason I'm thinking of ASICs.
If I use a scrypt multipool with an ASIC, what happens when the pool switches to a coin it can't do?
I like GUIminer-scrypt, as it just works. Tried cgminer and it was a horrid interface and I could never get it to do more than one GPU at a time. I'm a Windows user only, I don't like text mode stuff.
If people starts to break GPUs often due to mining, manufacturers will start to refuse product replacing, citing overclocking; honestly, i can't blame them, shall they go for this choice.
Scrypt multipools only mine scrypt coins, they cannot switch from scrypt to scrypt-n. At least for now.
I am a windows user too, and if you accept my suggestion, you should learn cgminer/sgminer/bfgminer commands, you can do amazing things with it. Things you can't do with guiminer.