Lets see I use mainly 4 OSes (if you group various linux distros). At work I use mainly OS X Lion, with VMware Fusion running whatever I might need (win7, winxp, various linux distros).
At home I have 2 PCs, both running Debian GNU/Linux (server & desktop, desktop being connected to the 47" TV set via HDMI). Then 3 Macs running MorphOS, and 3 MacBook Pro laptops running OS X Lion.
I have no trouble switching between OSes and I do that constantly at work (copypasting stuff between host and guest, handling everything via keyboard shortcuts etc).
As to network: I have 100/10 Mbit fibre coming to my flat. I have that connected to my Debian server boxen (it also has 10 TB crypto-RAID6 setup for backups and other confidential material, including time machine for all the OS X laptops). The box is sharing the connection (NAT) via 16-port gigabit switch and 300Mbps WLAN (laptops). I also have 8 TB RAID5 NAS box for movies (both the NAS and TV do DNLA so I can play stuff from the NAS direct from TV).
This is just part of the setup. Yes, I could use some extra room
