I did a fresh install of Ubuntu 8.04 on a Dell Inspiron E1705 to use at work (Windows 2003 network).
The first problem I noticed was the inability to download flashplugin-nonfree; connection would hang. I am also not able to go to adobe.com, macromedia.com, facebook.com, livejournal.com (I'm using LJ Mobile). There are a few random sites that I can't connect to that seem to hang while connecting to CDN servers. I don't know if this is the problem per se, but it is definitely common among the sites I tried to visit.
I took the laptop home and was able to connect to adobe with no problems and install the flash plugin.
Windows machines on this network can connect to these sites fine using Firefox and IE.
I tried adding various DNS server addresses, but it didn't seem to help.
I also tried plugging into a port on the router itself, which also didn't seem to work. I could browse around all day long, but would run into sites that would hang.
If it makes any difference, we have a T1 from Telepacific Communications.