Just sharing my experience with setting up VPN in WHS 2011.
I set up 2 HP proliant microserver using WHS 2011 (as per instructions available on this web site). Everything went well without any hiccup. I have talktalk fibreoptic broadband with 45 mbps down and 11 mbps up speeds. I set up vpn on my 1st server using instructions available on the internet. (Google 'How to Set Up VPN for Windows Home Server 2011').
I also set up L2TP/IPSec protocol in addition to PPTP and SSTP using instructions from http://www.ryanamos.com/?p=25
Everything worked perfectly and I could vpn to my home network from any platform (IOS, android, windows) without any problem and I could get on my vpn client over 10 mbps download speed (almost close to my ISP's upload speed). In fact I could brouse on the VPN client just like normal including watching youtube.
Amazed by the success of my vpn set up, I did install vpn similarly on the second server which was at my friend's house on BT infinity broadband with slightly better connection speeds than my ISP. Set up went well, could connect VPN clients without any problem, could do file transfer from local PCs and use RDP without any issues. But browsing internet was painfully slow or the pages did not load at all . Very few pages including google would load but bbc, youtube or most other web sites would just not load. A standard ping test was fine for all these sites. I checked all vpn settings with no success. After several months I happened to read an article about mtu size and vpn from a TP-link faq http://www.tp-link.us/article/?faqid=190
BT infinity uses PPPoE unlike talktalk which is IPoE. My friend was using a TP link router (having ditched BT HH3) with a default mtu of 1482. After doing the tests in the article mentioned, I found that the maximum mtu size without packet fragmentation was 1372. I changed the mtu on the router to 1370 and restarted it. Voila! vpn became fully funcctional instantly.
Prior to this there was no problem for internet access on the local net work and problem happened when internet access was attempted over vpn. May be vpn added overhead on top of standard packet size and caused problems.
Hope this helps somebody. 