LOL. Saw many questions and answers which are so ... well.

Hope my answer can help. Lazy to Quote again.

1- For 16GB microSD and 32GB micro SD, it does not cause lag if it's in the same class. Or technically slower in showing files and content. But comes to extracting, reading and writing, it's the same.
As after media scanning, it keep the cache file in reading. When loading content (in file manager),
what people say lag it's actually 32GB have more files to load (perharps 1-5secs if full 16GB and 32GB is used), but comes to read and write (capture pic, watch hd video, playing apps and games),the phone choose the content that you click and read and write in at the speed of the class of your micro SD.it still the same speed as 16GB as long it's the same class.
Except you compare different class of microSD.
2- HD GAMES in SD card. = You can play those HD GAmes, as when you play those games, android system will automatic turn off other "non-current-using" apps such as laucher and others, in order to get enough ram for your games. after you finish the games, it automatic regain back ram, and will extract back those apps such as laucher and etc. So for Gameloft HD games, it's playable. For myself, i got several games. See photo I attach below.

Additional information,
You must bear in mind that new phone from Samsung and LG offer 3 layers memory for phone which is internal memory, internal SD (/mnt/sdcard) and external SD (/mnt/sdcard/external_sd).
where other or old phone have 2 layers which is internal memory and external SD (/mnt/sdcard).

when download gameloft games, data file is save at default directory ( /mnt/sdcard/),
it is save to external sd card for 2 layers memory phone but comes to 3 layers phones (SGS,SGS2 and SGW),
it save to internal sd, so only 2GB can use for games. ( For us the SGW users)

must root to use 3rd party apps to mount or patch ur games apk file (change the default data directory save to mnt/sdcard/external_sd) only can move data files to external sd in SGW.
bear in mind. >,<

(I think this should include to the detail of the phones in top post, some people might don't know about this information.) ( Repeat this for 3rd times) LOLZ 
3 - No matter what laucher you use, when too many content and background services, it still cause lag or slowdown. It's normal in android. I got laucher 7, icecream laucher and twlaucher, switch to any other for fun.
and sometimes it lag after you play HD games or some apps that ate many ram.
so have to wait, and clear ram and also kill some background tasks.

I got 56 games, 20 HD games (actually just big files games and some gameloft games), and some add-on widgets and it slightly lag after games.

I just make a flick account and upload some screenshot.
Hope you guys can see it.

*btw, sorry that I can't make a video about SGW yet, as my bad "aunty" don't want borrow me her BRAND NEW camera. lolz.


SC20111207-081013 by andrew_wang916, on Flickr


SC20111207-081005 by andrew_wang916, on Flickr

SC20111119-212033 by andrew_wang916, on Flickr


SC20111119-211959 by andrew_wang916, on Flickr

Just Sharing. ;D  and not showoff. ( a bit la.  ) haha
And if install too many files, might have some slightly lag when play games too long,
or finish a apps or games. need to wait it to load back your laucher and other setting.