Slow? Well, SP, if that's the case there's no sign of it so far. Though I would say that wouldn't I.
The overriding issue for me is the Vista OS a hostile operating environment for 3rd party stuff. So far it has proved to be; I tried Opera and Firefox and both kept stalling, error reports, load error pop-ups, etc, etc, etc, etc. So I kept going with IE7&8 even though I know IE is cack security-wise.
Since installing SeaMonkey, firewall, antivirus, antispyware haven't filed any threats/quarantines in their respective history logs. With IE there'd be threats/quarantines logged every time I browsed.
I was reading a new review on the different browsers the other day and it basically said Seamonkey was Firefox 2 with loads of extensions slowing it down ?