Mine isn't slow or laggy. I find having less icons makes the phone faster (at least in terms of animations) so now I have 1 full page, and a 2nd page with 4 icons. No problems here.
However, I do desire upgrading to the iPhone 4. Just to have the latest device, basically. And because the vibrate switch on my phone is acting up A LOT. But it'll be summer soon and I won't need to put my phone on vibrate as I wont be in school during then, so I have a feeling I can wait. The iPhone 4 looks so nice. I should have bought one earlier, but now I'd rather wait. (people reporting that its laggy with 4.3.3). Plus, I have an iPod Touch 4th gen I can play with until then. If Apple releases new software for iPhone in the summer, that would probably pull me out until November (what latest rumor reports). But the rumors have it at that there won't be anything new in summer. I'm pretty sure I don't run out of RAM on my phone because when I do, it gets pretty nasty ... and I haven't seen that happen unless I have some very large games open (or too many apps open in general).
My 3GS was refurbished as of September 2010, so battery life is still amazing. I think I had 4 hours usage, 21 hours standby, with 65% left.
Well thats just me trying to justify waiting with my 3GS. 😛