[po-faced boring post alert] I love getting them, and with no irony whatsoever. I only wish everyone did them. I get quite annoyed with people slagging them tbh, because I assume people will be less likely to write if they think people are laughing at them.
Obviously it would be even more amazing if friends I no longer see very often, or which I'm maybe not that close to, sent me long personal letters, but if that's not possible, I'd much rather know what's going on in their lives in any way at all. My aunt does one that is 4 A4pages long, is she supposed to do a personal letter that long for everyone she knows around the world? No-one is forcing me to read it, but I like to because it's like talking to her, only better. I also hang on to them and read them again when getting out last year's Christmas cards to write this year's. I'm also rubbish at names, address changes and esp children's names, so letters like this help me update my diary and so on.
And I have a really close friend, who tells me so much intimate detail of her life I sometimes get embarrassed, and having her letter is useful because I know what is 'public knowledge' IYSWIM. Also reminds me of stuff about her life I'd forgotten, or not realised was really that important.
Anyway, maybe they're only a help to relationshipally-challenged people like me, but if you want to do one, don't be put off.