FWIW, I was with PlusNet for some time until I moved (and had a spell without any internet access, and there was no phone line, so I put off bothering). Although some who joined PN via one or other of my websites (for which I 'earn' 4 pounds a month in commission) have now left, quite a number still use the PN service and I get no complaints from friends (and my sister) who are currently on their service.
One downside of measuring satisfaction is that those who are unhappy are usually the vociferous minority. It's less common to see comments like "I'd recommend " compared with "service at has gone downhill" so even 90% being negative is unlikely to actually compared with the general feeling.
I've just recently arranged to get a BT line (free installation) and will, personally, be giving PN a try. I don't have the option of higher speeds with cable or from Sky / O2 / Be Unlimited / others.
I'll have to keep my line rental with BT for 18 months, otherwise I'd consider getting service for a year from Heart Telecom, which is offering the first 6 months for free, then 8.50/month (plus a tenner line rental) [but you do have to add VAT, and there's probably a one-off 30 pound setup fee.)
This is aimed at business customers, gives a static IP and higher priority than for home users, and offers a 'reasonable' amount of traffic (10 GB/ month)... That is reasonable unless her family does a lot of browsing / streaming (iPlayer, YouTube etc)
See here for their 'free' (for 'up to 8 Mbps') deal - the dates when this offer is valid come from an e-mail :
Starts: Monday 18th January 2010
Ends: Sunday 14th February 2010
On the loss of e-mail at PN - it's not that difficult for e-mail to be downloaded into a free/ cheap e-mail application - Windows offers Outlook Express or Outlook (if you have MS Office).
I would always recommend a person uses an independent mail service (eg Google Mail, or even one with charges like FastMail.net) rather than one offered free by an ISP, because one might decide to change at short notice, and it's not uncommon for an ISP to close the mail account when you stop paying for Broadband access.
If you are running a business you might choose to have mail in a web host mailbox (for collection by Office) and also forward a copy to a separate account (which means you can have an archive or emergency access, and if your home or office PC normally collects the e-mail, then if you are working away, or on holiday, you could use a web cafe to check for mail via the independent mail service (such as GMail.com)