i've been using the IE7 beta for quite awhile now, with no complications. it's adopted the ffox tabbed browsing which i've been a big fan of for... well... ever.
i also have ffox 2.0 and ffox 1.5. makes me pretty much a ffox ****. i prefer it over IE, just because it's smaller and has a lot of choices when it comes time to personalizing. i like that. i only keep IE around for those times when a site has been designed strictly for IE.
so, i'll update it and see if it works or breaks.
V***V