Additionally, you need one IP address per https website you want to host. This isn't an issue with IPv6 (Yay IPv6) or when using a webserver/client that can use Host headers before the SSL transaction (which all older browsers do NOT support). The main problem is that not everyone has a metric 'shitton' of IPv4 addresses and the software isn't wide spread enough to reliably host multiple SSL websites on a single IP with vhosts.
Now, there are some other circumstances that people will state that isn't really valid IMO. Some people will state that SSL certs cost money. I recently purchased a handful of wildcard certs from StartSSL for $20 (IIRC). The only thing that cost money was the identity check and even that was pretty painless. I highly recommend them for small/medium businesses or individuals. Their root certs are in iOS, Android, RHEL as far back as I cared to check (RHEL 4), Windows, Ubuntu, etc. </slashvertisement>