I've run into some odd quirks with IETester and similar tools where they don't run exactly like their actual brethren. It's probably fine for the 95% case, but

I've run into some odd quirks with IETester and similar tools where they don't run exactly like their actual brethren. It's probably fine for the 95% case, but that other 5% can be infuriating. It usually manifests itself as the page working fine in IETester and your customer being adamant it's broken in IE 8 (or whatever).