I recently moved from Plusnet to Sky.
I changed as I got tired of Plusnet’s traffic shaping which slowed the speed to a crawl in the evenings and getting grief when the usage occasionally got to 12gigs in a month despite having a supposed 20gig limit.
The change to Sky was completely painless – I was given about 3 weeks notice after I gave them the migration number. The changeover occurred on the day they stated and I was without broadband for effectively no time at all as I was at work when it happened.
With Sky I have had no slowing of the service in the evening at all and I am very happy so far.
Be aware that all of Sky’s broadband packages are going to increase by £5 in the next year or so according to a letter I received in December.