I will be going to 4 different countries in Europe (all long distance trips) and I've read conflicting opinions on whether to buy a Eurail Saver Pass for 4 countries in 8 days, rather than buying the tickets online?
I did my own calculations and so far, the Eurail Saver Pass has come out cheaper. And Eurail Saver passes are all 1st class, the ones I've researched on the Net are all 2nd class and still the total comes out more expensive.
Can someone point out if I missed anything?
And can someone tell me if making a reservation won't be a problem upon the day of the trip itself?
Yes, the calculations are about right. Especially when you are taking long-distance night trains Eurail comes out a lot cheaper than point-to-point.
I cannot tell you whether making reservations on the same day is a problem, because that depends upon the day you travel. Think of season, major holidays, fairs that attract lots of business travellers, universities starting up,... Generally it is so that as long as you can still buy tickets and reserve couchettes/sleepers/seats over the internet, you won't have any problems. If you are in the same country, you can also reserve for a train that leaves from another city.
Which countries are you doing??? Eastern Europe may work out cheaper to buy point to point but Western Europe it is a close call. When calculating costs check reservation fee / couchette fees etc for both version of tickets. If you are happy to just jump on a train as it comes by and are not fussy about the seat then Eurail can give you more freedom to travel and if the money starts to dry up at least you know you have a ticket to get you to the next point of call.