I am planning on spending some time in Vienna area late April. Has anybody followed the Danube from Vienna to Linz? Boat vs Bus? I hear it is beautiful. Any hints or suggestions on that trip. How long should I take?

I don't think the boats run in April, however, here is their site: http://www.ddsg-blue-danube.at/
I don't know if the boats go all the way to Linz and really the furthest you really need to go is Melk. Linz is pretty industrial although it does have a charming old city center. Try my site for some ideas: http://alexstarke.tripod.com/
If the boats are not running you might consider the train instead of the bus. The only real way to experience the Donau is by bicycle, the real adventure. Cars, bus, train, or boat are okay but to really experience the Danube, its villages and people, cycling is the only way. If you want more assistance on cycling you may e-mail me through my site.

This last summer we drove on the south side of the Donau from approx. Melk to Passau, stopping at Linz for lunch, and overnight at Passau, then drove the north side back to the Melk area before cutting north for two days.
For some reason, even tho it was the same stretch of river, north vs south sides seemed sufficiently different.
We found it quite enjoyable on both sides. We drove what I would call the shore road (no -bahns). Vienna would be perhaps 1-1/2 hour from Melk, and Melk perhaps 3 hours from Passau straight thru. That's just perception, others may have more accurate estimates.

We drove along the river from Melk to Durnstein and stayed overnight. Even staying one night I didn't feel rushed. We had lunch, walked around and then took a couple hour boat ride on the river. After we walked around more and ate at a wine bar outside near the vines...having alot of little dishes and great wine. In the morning I climbed up to the ruins of the castle which was amazing...great view. I would highly recommend staying there. The town is very charming. THe hotel we stayed at was SAENGER BLONDEL. It is suppose to have a good restaurant also but it was closed the week we were there. The breakfast was good.

I would suggest that you rent a car to travel along the danube.
As posted,a good road runs on both sides of the river( to me the north side is nicer) Many small villages and guest houses to enjoy and of course wine and vineyards.
The area fom Krems to Melk is the most beautiful and is well worth a good visit.
Even with a car ,it is well to take the tour boat between some stops, like Melk to Durnstein and return.
Boats do run from Vienna to Melk.But the journey from Vienna as far as Krems is not very interesting and the trip takes a full day.
The area upstream from Melk toward Linz is not so interesting.
If time is no problem, a bike can be rented( of course go downstream)
April is not a busy tourist time in that area and some places will not be open.
Last year, the warm weather caused the fruit trees to bloom early. Perhaps you
get the same weather.
An alternative is to take the train. It runs numerous times daily from the Franz Josef Bahnhof to Krems. You then transfer to a local train that runs on the northside of the river through towns such as Loiben, Durnstein,Spitz etc. You can stop in any town and get the train back later or take the boat some way and then back by train.
At least one day should be spent there. 2 would be better as a trip through the monastery at Melk should not be missed.