Its fine until a java applet or some script or flash loads, then the whole thing grinds to a halt. I never had issues with 1.5 other than the diabolical number of crashes (at least 2.0 saves sessions properly...)
If they spent less time on stupid bloody flashing, scrolly, zoomy, swirly transparent menus and glowing buttons and graphical bullshine and more time fixing bugs it would be awesome. Instead they pander to the people that look at Google, check their hotmail and a news site then close the browser but still demand novelty crap plastered everywhere, not people that work and develop using it every day with dozens and dozens of tabs open.
Get it sorted with bugfixes, speed, functionality. In that order.