I use IE7 and am very happy with it. If you are still using IE6, I recommend 7, if for no other reason than the security updates is has - not so much for holes that are patched, as I never fell for the Firefox hype that using IE automatically made me vulnerable - But for the much improved BHO (add-ins) manager, the very effective (but not over-zealous) pop-up blocker, and excellent phishing filter.
I was worried that ieSpell would not work and I can't live without that. But it integrates perfectly with IE7 as well.
I have had no problems accessing my on-line banking (Wells Fargo and a local bank), credit card accounts, two credit unions, or my 401K/broker secure accounts.
I have noticed no performance issues at all - except it may even be a little quicker (but I will not rule out wishful thinking or power of suggestion for that - but performance was not degraded).
Tabbed browsing is something I never yearned for, having experienced it years ago in Netscape, before Firefox arose from ashes. However, now that I have gotten used to it, I like it. I still open with just one home page, but I can easily open different groups of home pages (all the forums I help out at, for example). And I love
Quick Tabs.