Sparrow is faster, doesn't take up the same memory that a tab does, and it's faster to find the icon in your Dock than dig through 40 tabs, plus it's nice to be able to quickly switch between Gmail/Google Apps accounts.
I used to use this with Gmail, but switched to Sparrow a few days ago. I've been interacting with my email in a much faster and more fluid way since, which wasn't possible using Gmail/Fluid.
I use fewer site-specific browsers than I otherwise would because of memory usage, but these days many of us have 4-8 GB RAM and running one or two SSBs doesn't break the bank, so to speak.
Chrome's notification boxes have three major complaints from me:
A. They don't automatically close. (I think you can change this for each web app individually, but I would like a browser-wise setting). This wouldn't be a big issue, if not for...
B. The close button is freaking tiny. I can dismiss Growl notifications by clicking anywhere on them, which is much nicer on a laptop than trying to move to a small button.
C. The notifcation windows resemble what Apple calls panels. [1] The problem is, "Panels float above other windows and provide tools or controls that users can work with while documents are open." [2] The user isn't meant to be closing panels often, which is why the title bar can be small. Chrome's notifications feel out of place in that regard.
