You normally don't notice tbh. Switching PDS is entirely invisible to the frontend. There's a lot of self hosted PDS users (since it's basically a small go router + sqlite) but there's also bigger community PDS projects being spun up including blacksky and northsky.
As for frontends, there's a bunch of them and a lot of them focus on changing the UX. But for self hosted "bluesky", there is https://deer.social which is a forked client that still relies on the bluesky appview/backend and there is https://zeppelin.social which is downstream of deer social but also runs their own appview independent of "big bluesky".
If you go to that URL, you'll see the landing page for the atproto PDS software.
Edit: Ah, and seems Kuba is hosting a directory of profiles using their own PDS as well, lots of examples over there: https://blue.mackuba.eu/directory/pdses
Biggest one right now (excluding the default one) seems to be atproto.brid.gy, which has 40393 accounts.
Not only is the bluesky network highly centralized right now, its UI is designed to perpetually lock users into the main bluesky server. Even if you use your own identity, when sharing the URLs to the posts via the UI, the URL defaults to bsky dot app domain, which will break if the author ever moves to a second server.
2. If you change your handle (for did:plc, did:web can't do this because DNS) it used to break links but nowadays this isn't a problem because handle resolution respects historical handle naming (I think it works by post+handle age but I can't remember).
3. Also if you share posts using the did syntax instead of handle syntax (which bluesky seems to be slowly changing over to, at least profiles do this now), it's stable regardless of handle changes.
4. If you want to switch frontends, you can use an extension or app like at://wormhole to do so. UX for this should improve over time but that's a big "eventually".
5. Hopefully the at:// URI format catches on but that's a long ways away given that browsers make using custom URIs an absolute nightmare.
The default Bluesky frontend uses bsky dot app URL when you use the "Copy link to post". Now if one day, you lose trust in this server and switch your PDS, this link continue working depends on this very non-trusted server. If this server is profit-seeking, it can break such links.
An extension or another app is not the solution, and neither is the new at:// URI format, because what matters is the relationship the default server sets up with its majority of users. Most bsky users will lose their traffic to their own posts and therefore will be locked-in, cementing this one server to be the dominant one in all perpetuity. We will therefore get all the patterns of monopolistic abuse that we have seen elsewhere.
