Bottom Bracket/General Frustration advice please?

Prior to Xmas I bought a new bike at a shop which is not my LBS but
nonetheless seemed ok. I wanted a second bike for general buggering about
on. They were selling it quite cheap whereas my LBS has a reputation for
being rather pricey.

However, having now done a good few hundred miles on it I have noticed that
the shifting, particularly at the front, continues to be very hit and miss
and the bottom bracket creaks like hell, which is driving me absolutely
nuts. I initially put the shifting down to general cable stretch and duly
took it back to the shop (3rd time) where I bought it who inform me that
they again adjusted/stripped it all and that the creaking was due to the
aluminium/steel relationship between frame and bracket and that this was
normal. They have now made 3 attempts to sort it out and its no better. The
set is Tiagra and it generally starts after about 10 mins riding - hence the
fact it doesn't happen on the stand or outside the shop!!

Anyway, first ride out today post latest 'fix' and the problem is worse than
ever. Added to which the bloody chain kept coming off. I know I should take
it back but I have lost confidence on the shop's competence and am looking
at other options:

1. Swapping the bike altogether - shame as I really like it. But also like
the look of the Cannondales that get rave reviews, except that I ride only
for fitness and around 80 miles per week - I dunno if these would be a bit
OTT for me?

Can anyone comment on the R500? Must admit I tend to feel more comfortable
on a flat bar though so any other recommendations welcome.

2. Upgrading the bottom bracket/chainring and derailleurs to something like
Ultegra - would this make a difference? Also how much would this cost
(roughly?)

The moral of this story is of course to deal only with your LBS. They may
be dearer but at least you can build a relationship with them. Now I have
to go in red faced and admit I 'cheated' on them and bought from a
competitor.......I know I will have to pay the price. Upside is that their
mechanic is red hot and can fix most stuff.

Cheers.

S