It only takes a minute or two to update WordPress in my experience, so it won't take too long.
I always try to keep WordPress and all my online programs updated since the updates sometimes contain security updates to make it harder for hackers, and spammers to register on your site to hack or spam. Recovering from a hack, or spam attack can be very time consuming.
Wow, I can't believe WordPress 3.2.1 already came out, so soon which might fix your slow editor performance.
Indeed, new software can have new hacking problems, but there are usually more hacking problems and spambot problems with older version of WordPress like WP 2.0.
No, I don't experience any lag when typing up new articles. I notice the new WordPress to be faster. I think it is your open tabs slowing down your article.