I pay the server admins for feddit.uk (the instance this community is hosted on) to help with hosting costs because I think they provide a valuable service. Currently I am not paying towards Lemmy (I do pay towards Mastodon development however) but I may start doing that in the future.

My £5 a month to Feddit.uk and £1 a month to Mastodon isn’t much but it’s orders of magnitude more than Reddit and Twitter would have earned from my (adblock using) eyeballs before so hopefully a few of us paying a few pounds/euros/dollars directly is enough to support the services.

Edit (approx. one month later): I am now supporting Lemmy development directly, ~$5 a month which I hope makes it sustainable if enough people contribute.