I've never waited more than 20 minutes for a bus at WL. From what I understand, when using the bus service it is the norm to get your bus anywhere from 1-20 minutes. Usually we waited about 5 minutes.
But of course, once we had to get to Boma for a 9am breakfast, we only left ourselves like 45 minutes to get there and needed to get a bus to MK to switch to a AKL bus-we waited the FULL 20 minutes at WL for our bus! Every minute I was saying to myself in my head-"we should have taken the launch!" and alternated that with "should we try to get a taxi??"

It's like a roll of the dice to take the launch or the bus! BTW-we ended up about 15 minutes late to our ADR-they got us in within 5 minutes, no problems...but we did learn our lesson-when transfering to get from one resort to another-you really need to give yourself an hour! We had such quick service on the buses and boats earlier in the week that we thought we could make it in 45 minutes-but you really can't rely on that.
One weird exception of waiting more than 20 minutes...during Christmas week we waited at MGM for a bus to WL for like 45 minutes! This was at like 12:30pm. It turns out that there was such a huge back up of cars trying to get into the MGM parking lot that even the buses were stuck in the gridlock and couldn't get in to get us! I'm a little surprised that there isn't a "special" WDW bus enterance/exit to and from the parks.
Overall, I've always been fine with the WL bus/boat service. One "complaint" I would have is that sometimes you do share a bus with either FW, CR, Poly, and GF. But, then again, Poly, CR, and GF often share busses, BC/YC, BW, Swan/Dolphin share busses and boats...That is fine I guess, but my problem is...you never know if/when you will be sharing and with how many resorts-so you aren't really sure about timing. If you are trying to get to a park for a specific time this would be a bit of an issue I guess. Most times, we had our own bus...but sometimes we would have any combination of sharing. One day direct to Epcot, another day we would pick up FW before we went to Epcot. Anytime we shared with the monorail resorts, it was always on the way back from a park and WL was always the first drop off everytime...that didn't seem very fair to them since WL didn't have to sit on the bus while they were the last to get on(and since they were paying A LOT more for their resort than I was paying for mine!

)
It seems like WL gets a lot of "transportation trashing" sometimes...but I don't think it is better or worse than any other resort, somedays you get a break and that EPCOT bus is there right as you walk down...other days you wait a little. Even on the monorail resorts...you could be waiting a bit on that monorail loop. I took the mororail from MK to GF and it took me like 20 minutes! This was with the monorail right there ready to board as soon as we walked up to it-no waiting in line at all-and no "hold" between resorts either.
I think general rules wherever you stay:
1-20 minutes for busses/boats, 1 hour to transfer resort-park-resort.