Combining filters and labels with the "Multiple Inboxes" labs feature is even better. I've got labels+filters for each of the customers of my consulting/contractor business and have the ones for whom I'm currently doing projects visible via the multiple inboxes, which gives me the latest info, within its context, all on one screen. Brilliant.
Admittedly, it takes some time getting used to. I hated the Gmail UI when I first started using it and would use Thunderbird instead whenever possible. These days the only negatives I can think of are:
* paranoid policy for attachments. No exes, no zips with exes for sending or receive. This can be REALLY annoying when working on desktop apps for customers. I would upgrade to the paid-for version if that let me switch this off.
* reliability. About once a week either IMAP or the web interface go down. Almost never both simultaneusly, though, and rarely for long, so it's tolerable.
Sometimes when I'm searching tech discussions with colleagues/clients, etc, I just want to see the emails with the relevant terms, not all 75 emails in the conversation in a big cumbersome list.
With well-organized folders, I can, and more.
You should give it a try. It's a new way of working...