Yeah, some of the shops start closing from about 4:30, but other than that Liverpool's pretty much the same on Sunday as it is on Saturday. If Messrs Ed, Stress and Back (or any other boarders, for that matter) fancy meeting up for a pint at some point, PM me and we'll arrange something.
Also, ignore most of Peter's post. Liverpool is approximately as rough as any other similarly-sized city. No more, no less.
The city centre is busier on match days and post-match football crowds are generally drunken, rowdy, aggressive nob-ends wherever you go.
You probably will attract negativity if you go around critiquing the local accent, so best to just smile nice and drink up.
Other than that, have fun!
-Scousebast