3 Chrome Beta windows, with 17, 14, and 1 tabs open. 1 Chrome Canary window with 2 tabs
A good number of these tabs have not-very-light applications open like Gmail, Google spreadsheets, and some YouTube vids.
If you say to yourself, "oh, let me go check out Firefox compared to this," and launch it with one tab, do a quick Google search, and then determine, "hey, this is way faster," well... yeah, I wouldn't be surprised. Not only do you not have multiple windows and tabs open, but if you haven't used it in years you've probably got a pretty small cache not bogging you down.
Personally I've never actually noticed Chrome's performance to have any issues. Maybe because I have 12 gigs of RAM and an otherwise decent setup. On a more constrained system perhaps problems start to show themselves more easily. But are you sure that those same problems don't also appear in other browsers, given you're using them as intensely as you've been using Chrome this whole time?
I'd really love to see some browser comparison stats that go in-depth on this. Basically the only numbers you ever see these days are javascript rendering scores, and I feel like that's a really poor way to determine a browser's overall speed and efficiency. It doesn't account for how long it takes to open a new tab (like .01 seconds vs .3 seconds, which IMO is a big difference), scroll lag, startup time, etc, and it certainly doesn't account for how and if browsers become bogged down by real-world use.
I fear that users may be making similar snap judgments by comparing on the basis of quick open-and-go tests, instead of actual in-depth testing. First impressions are everything. You may find yourself five years from now using a browser that is actually slower than you were using previously, but you maintain your use of it because one time five years ago you opened it and loaded a page and it was faster than the encumbered incumbent.