I'm in similar position of choosing a Fibre Optic ISP since I'm in rolling monthly contract with O2 at the moment. O2 isn't bad for my connection but it doesn't have fibre!!! I have been observing various potential Fibre ISPs in my area, including BT Infinity 2, Sky Extra-Fibre, and PlusNet. I was initially leaning towards Sky Extra-fibre UNTIL I seen this in the Sky Forum :
This "Half-speed" issue seems to be happening randomly and been happening for quite a few months now. I'm not scaremongering but it does make me hesitating to pick SKY until their issues can be fully resolved'. PlusNet seems to be fine EXCEPT their 250GB cap per month does worry me as my family collectedly would tend to use around 7 to 8GB daily, which is around 240GB per month at the moment. However I have plan to try Netfix for streaming movies in near future though! BT Infinity is a mixed-bag as well.
Intel E4300 OC with 2GB RAMs,Speedtouch 585 Modem/Router and Windows XP Pro
O2 Standard ADSL2+ Broadband!