I agree with Matt in that it appears the Jagger update is pricipally about how Google now treats reciprocals but I think way before Jagger, reciprocals had 'had their day' so to speak and folk were realising that apart from the issue of PR transfer it was much better to gain one-way links instead.
As far as sitewides go my thoughts are that it's a matter of moderation plus a dose of Google luck as well. By Google luck I mean that whatever measures Google decides to implement at any given time it's often down to 'luck, good or bad' as to whether you come off better or worse.
We're all aware that Google sees 'comment tags, keyword abuse, guestbook spamming, link farms' etc etc as methods used by spammers to artificially inflate a sites ranking so we don't do it for fear of being penalised by Google but... they're still in the search results every day, try searching for anything related to porn or viagra for examples.
Google appears to have as many spam sites in it's index as non-spam ones so I can only conclude from this that Google can't actually 'control' spam but merely sends out warnings. These warnings sometimes cover the arena of links whereby Google stamps on a sufficient number of sites that folk start to mention it in forums etc, then they discover a similarity (in the case of Jagger it seems to be recips) and then folk react to that.
There's no doubt though, that there's lots of recip sites that haven't been hit by Jagger and probably will not notice the update.
Moderation ?
To my mind, a web designer who adds a link to each page of his/her clients website has no problem. It is after all, a copyright statement and I cannot see anyone being penalised as a result (guessing)

.
I do however, see a potential problem if the site is large (dynamics in particular) and if the links are in the footer area as I think Google has got this one well sussed (sudden and unatural bunch of hrefs at the bottom of the code) must raise a flag, and if sufficient flags are raised bye bye.
But again, I know of clients who have loads of sitewides and don't get caught whilst others with only a few hundred do?
So if you stay in the 'middle of the road' and don't overdo things you should stay lucky.
If you must go for sitewides I'd suggest
* point the anchor text towards the home page for 60% of the links
* vary that anchor text by using a mix of related keywords
* point the other 40% to a variety of pages throughout the site
* use mixed anchor text pointing to those pages but do not use non relevant anchor text, only that which matches the topic of that particular page
* use the content area of a page instead of the footer area this looks far more natural
* above all, build the sitewides gradually.
Lastly, Good Luck
Ray
(my new years resolution is to make shorter posts)